Slide 1 - BITS Pilani

Wireless Systems and

standards

Chapter 11









1

Applications of wireless

• Traditional phone systems

– Replacement of wired loop

– Displacement of PSTN network by cellular

carriers

• Integrating the voice and data communications

as the cellular system evolves

• Replacement of wired communications between

fixed points

– Fixed wireless access

• In local loop replacement (for example DSL

lines)

• In trunking applications 2

Applications of wireless

• Replacement of wires within home, offices etc

(Wireless LANs)

– Wireless LAN in the home to connect multiple

PCs

– In office buildings to extend existing wired

networks

• Local multipoint distribution systems









3

Standard setting bodies in Wireless



• ITU-T

• IEEE for Wireless LANs (802 committee)

– Examples are: IEEE802.11, IEEE 802.15, IEEE 802.16

• European Telecommunications Standards Institute

(ETSI): GSM

• EIC: Electronic Industry Association:

– Examples: Interim std IS-54, IS-136 (TDMA in 800-900 and 1900

Mhz band)

• TIA: telecommunication Industry Association IS-95

CDMA

• Cellular Telecommunications and Internet Association

(CTIA)

• The Open Mobile Alliance (OMA),



4

Cellular technologies evolution

• Broadly classified as

– First generation

– Second generation

– Two and half (2.5 G) generation

– Third generation

– Already talking about 4 and th generation









5

Cellular Technologies Evolution Cont‘d

• First generation cellular systems (analog)

– Advanced Mobile phone service (AMPS)(1983)

• Frequency band: 824-894 MHz, channel BW of 30 KHz, FM

modulation

• Frequency division multi access

• Mobility to the phone service

– Narrow Band Advanced Mobile phone service (NAMPS)(1992)

• Same as AMPS, except uses channel BW of 10 KHz

– Total Access Cellular system (Mostly in Europe) 1985

• Frequency band: 900 MHz, channel BW of 25 KHz, FM modulation

• Frequency division multi access

• Also called European Total Access Cellular System

– Nordic Mobile telephone system

• Frequency band: 450-470 MHz, channel BW of 25 KHz, FM

modulation Developed in 1981. Uses FDMA

• Freq band: 890-960 MHz, channel bandwidth of 12.5 KHz FM

modulation Developed in 19861. Uses FDMA

6

Cellular Evolution (Cont‘d)

• 2ndgeneration Cellular system (Digital)

– Global System for Mobile Comm. (GSM) 1990

• Frequency band: 890-960 MHz

• Channel bandwidth of 200 KHz

• Uses Time division multiple access (TDMA)- 8 TDM channels

on one freq carrier

• Modulation : GMSK (Gaussian Minimum shift keying)

– United states Digital cellular (USDC): IS-54/IS136 (also known

as digital AMPS) 1990

• IS-54 and IS-136 are standards for TDMA American Digital

Cellular.

• Frequency band: 824-894 MHz, and 1.8/1.9 GHz

• Multiple access method (TDMA/FDM)

• Channel Spacing: 30Khz

– Supports 3 time slots

• Modulation: DQPSK (Differential Quadrature phase shift

keying)

• Channel Bit Rate: 48.6Kb

• Used in USA, South America and Australia



7

Cellular Evolution (Cont‘d)



– Pacific Digital cellular (PDC) in Japan 1993

• Frequency band: 810-1501 MHz

• Multiple access method (TDMA/FDM)

• Channel Spacing: 25Khz

• Modulation: DQPSK

– CDMA-One (IS-95) 1993

• Frequency band: 824-894 MHz, and 1.8 to 2.0

GHz

• Code division multiple access (CDMA)

• Channel bandwidth 1.25 MHz

• Modulation: QPSk/BPSK (quadrature phase shift

keying)

• Deployed in USA, south America, Korea, Japan,

China and Australia

• In general all 2G technologies have better spectrum

efficiency as compared to 1 G 8

2nd generation Technology









9

AMPS and ETACS

AMPS (Advanced Mobile cellular system)

ETACS (European Total Access cellular system)

AMPS system

• Uses 800 Mhz band (initially a total of 40 MHz was allocated to

mobile communication, later was extended to 50 Mbps, 25 Mbps in

each direction)

• First implemented in Chicago to cover approximately 2100 square

miles

– Used large cells and omni directional antennas to minimize equipment

needs

• The AMPS system uses 7 cell reuse pattern with provision for

sectoring and cell splitting to increase capacity when required.

• Subjective tests indicate a S/N ratio of 18 dbs for a statisfactory

performance

• Smallest reuse factor that satisfies this condition with 120 degrees

sectoring is 7 cell reuse.

10

AMPS and ETACS



• In US Duopoly was deployed, but other parts of the world did not

follow that. In US each provider ( A and B) used 416 duplex

channels each. The other parts of the world deployed a single

carrier in the markets.

• The freq allocations vary from country to country

• The Air Interface standard is identical thru the world.

• Each system has System ID (SID). Provider A has been assigend

odd SID numbers while provider B is assigend even SID numbers

ETACS

• Developed in mid 1980s

• Similar to AMPS, but uses 25 Khz channels.

• Mobile identification number (MINs) are formatted differently

– Need to support different country codes thru Europe, as compared to

area codes in Europe







11

AMPS overview

• Uses FDMA/FDD for Radio transmission

• Reverse link: 824 to 849 Mhz

• Forward link: 869 to 894 Mhz

• Channel assignment ; 30 Khz

• Separation of 45 Mhz between forward and reverse

channel.

– This allows use of inexpensive, but highly selective

duplexers in the subscriber units

• Max freq deviation +- 12 Khz (+- 10 Khz for ETACS)

• The control channel TX and Blank and burst

transmission use data rates at 10 Kbps

• These data streams have max freq deviation of +- 8 Khz

• The Base stations have tall towers, supporting several

receiving antennas, and have TX antennas that radiate a

few hundred watts of effective radiated power

• Each Cell typically has one control channel transmitter,

that broadcasts on this channel 12

AMPS overview (cont‘d)

• Each cell has one control channel receiver

– This reverse channel is used for call set up.

• Each cell also supports 8 or more duplex channels

• Commercial base stations support as many as 57 duplex

channels

• Actual number of Voice channels and control channels

per cell varies from implementation to implementation

– Depending upon offered traffic, maturity of the system

and locations of other base stations

• Actual number of base stations also varies.

– In a rural area there may be only one cell tower

– In urban areas there may be several hundred base

stations

• AMPS is a hybrid system, combing digital signaling on

the setup channels and on the voice channel when it

uses blank and burst. Voice traffic, though, is analog.

13

AMPS Overview (Cont‘d)

• Each base station transmits digital data continuously

using binary FSK at 10 Kbps, on the forward control

channel

– Idle subscriber can lock on to the strongest FCC

– All subscribers must be locked on to a FCC before it

can originate/receive a call

• The reverse control channel (RCC) receiver at base

station continuously monitors the RCC for transmissions

from mobiles that are locked on the matching RCC.

• IN US there are 21 control channels each for Provider A

and B. The Control channels are standardized

throughout the country.

• Thus a mobile subscriber needs to scan only a few

control channels to determine the best serving base

station.

• The service provider must make sure that the

neighboring base stations are assigned control channel

(s) that do not cause adjacent channel interference to

the subscribers that monitor neighboring base stations. 14

AMPS Overview (Cont‘d)



• In each US Market the ― A‖ provider is assigned an odd

system Identification number (SIN), while ―B‖ provider is

assigned an even system Identification number (SIN),

• SIN is transmitted every 0.8 secs, on each FCC, along

with other data such as

– status of the cellular system.

– If roamers will be automatically registered

– How power control is handled

– if other standards such as N-AMPS or USDC can be

supported by the system

• In US mobile subscribers either access system ―A‖ or

―B‖, even though technically the subscribers can access

both.

• Each System ―A‖ or ― B‖ supports 416 channels, out of

which 21 are uses as control channels

15

ETACS overview

• Uses FDMA/FDD for Radio transmission

• Reverse link: 890 to 915 MHz

• Forward link: 935 to 960 MHz

• Total number of channels supported : 1000

• Max freq deviation +- 10 KHz

• The control channel TX and Blank and burst transmission are at 8

Kbps

– These data streams have max freq. deviation of +- 6.4 KHz

• ETACS supports 42 control channels. ( Since no duopoly)

• ETACS uses area identification numbers instead of SIN

• ETACS users can access any control or voice channel.









16

AMPS : Types of Channels

• Control channels

– Reverse and forward control channels

• Control channels are used for call set up

• Registration

• Paging ( Notification of an incoming call to a mobile)

• Voice channels (Reverse and forward control channels)

– Voice signals

– Supervisory audio tone (SAT)

– Signaling tone (Used for sending a signal from a mobile

indicating call termination)

– Blank and burst ( The voice transmission is suspended, and data

is sent may be to effect a hand-off)





17

Call Handling in AMPS/ETACS

• Mobile registration process

• When a mobile is powered on it runs a self diagnostic. Then it starts to scan

the forward control channels. It picks the cell with strongest signal. Mobile

scans every 7 secs, or when signal strength falls below a certain threshold.

• Once it picks the strongest signal, it decodes SIN to determine if it is at its

home location.

• If too many errors it will pick next strongest signal



• When MS has successfully camped on to a FCC it transmits a message

which contains info such as Electronic serial number (ESN), its phone

number, its home system ID etc. The mobile sends this info in the RCC.

• The base station sends this information to MSC, which consults with various

databases to check the info out.

• If everything checks out the mobile is ready to either make a call or receive

a call







18

Call Handling in AMPS/ETACS (Cont‘d)

Mobile receiving an incoming call

• Mobile continues to monitor control channel.

• If there is an incoming call for this mobile, a page is sent by MSC on all the

base station‘s FCCs. The page includes the mobiles MIN.

• If the intended mobile receives this page, it will send an ack on the RCC.

• When MSC receives the ack, the MSC directs the base station to assign

FVC and RVC to the call..

• The base station also assigns to the subscriber unit a supervisory Audio

tone (SAT), and voice mobile attenuation code (VMAC)

• After the RVC and FVC assignment the mobile moves to these new

frequencies, and voice transmission can proceed. Also during a call, if any

signaling is required it is done on the pair of voice channels

• The SAT is transmitted continuously on both the FVC and RFC.

• The VMAC instructs the mobile to transmit at a particular power level.

• Once a call is up on a voice channel, all signaling is done on the voice

channel via a scheme known as "Blank and Burst". When the site needs to

send an order to the mobile, such as hand off, power up, or power down, it

mutes the SAT on the voice channel. This is filtered at the mobile so that

the customer never hears it. When the SAT is muted, the phone mutes the

audio path, thus the "blank", and the site sends a "burst" of data. The

process takes a fraction of a second and is scarcely noticeable to the

customer. Again, it's more noticeable on a Motorola system than on

Ericsson or Lucent. You can sometimes hear the 'bzzt' of the data burst." 19

Call Handling in AMPS/ETACS (Cont‘d)

Mobile receiving an incoming call

• For blank and burst mode data transmission, FSK is used by both the base and mobile station in

blank and burst mode to initiate handoff, to change the subscriber power , and provide other

system data.









20

Telephone Call Made to A Mobile User



Incoming BS

Telephone call

2 MS X

Step 1 26 37

PSTN

MSC 5

BS

4

Step 1 – The incoming telephone call to Mobile X is received at the MSC.

Step 2 – The MSC dispatches the request to all base stations in the cellular system.

Step 3 – All the base stations broadcast the Mobile Identification Number (MIN),

telephone number of Mobile X, as a paging message over the FCC throughout the

cellular system.

Step 4 – The mobile receives the paging message sent by the base station it monitors

and responds by identifying itself over the reverse control channel (RCC).

Step 5 – The base station relays the acknowledgement sent by the mobile and informs

the MSC of the handshake.

Step 6 – The MSC instructs the base station to move the call to an available voice

channel within the cell

Step 7 – The base station signals the mobile to change frequencies to an unused

forward and reverse voice channel pair. .(Sends SAT, Voice mobile attenuation code)

and At the point another data message (alert) is transmitted over the forward voice

channel (FVC) to instruct the mobile to ring. 21

Now the call is established and conversion can proceed)

Call Handling in AMPS/ETACS (Cont‘d)

Mobile initiating a call

• When a subscriber unit initiates a call, the mobile unit sends an originating message

on RCC.

– The originating message includes

• Subscriber MIN, ESN, station class mark and the destination telephone

number

• The station class mark or SCM tells the cell site and the switch what power

level the mobile phone operates at. The cell site can turn down the power in

your phone, lowering it to a level that will do the job while not interfering with

the rest of the system. In years past the station class mark also told the

switch not to assign older phones to a so called expanded channel, since

those phones were not built with the new frequencies the FCC allowed.



– If received correctly at the base station it sends this info to MSC

• MSC checks out the information to determine if the subscriber is a registered

user,

• Connects the subscriber to PSTN

• Assigns the call to FVC and RFC, with specific SAT and VMAC

– This info is sent to the subscriber units, who switches to the new freq pair, adjusts

it TX power level and returns the SAT back.

– During the call MSC will issue a number of blank and burst commands







22

Call Handling in AMPS/ETACS (Cont‘d)

3

Telephone call

Originated by a mobile

PSTN MSC

1

2

Mobile initiating a call



• Step 1 – When a mobile originates a call, it sends the base station its

telephone number (MIN), electronic serial number (ESN), and telephone

number of called party. It also transmits a station class mark (SCM) which

indicates what the maximum power level is for the particular user.

• Step 2 – The cell base station receives the data and sends it to the MSC.

• Step 3 – The MSC validates the request, makes connection to the called

party through the PSTN and instructs the base station and mobile user to

move to an unused forward and reverse channel pair to allow the

conversation to begin.



23

Call Handling in AMPS/ETACS (Cont‘d)



• What happens when all the voice channels are busy?

– The MSC will hold PSTN line open, and instructs the current

base station to issue a directed retry to the subscriber on FCC.

– A directed retry forces the MS to switch to a different base

station, fro voice channel assignment

– Depending on propagation conditions, location of a subscriber

unit and the current traffic in the base station the directed retry

may or may not work.









24

Call Handling in AMPS/ETACS (Cont‘d)

• While voice channels are in use, three additional signaling

techniques are used

– The supervisory signal audio tone (SAT); it always exists during voice

traffic except blank and burst

– The signaling tone (ST)

– Blank and burst wide band data (allow the adjustment of power levels, or

initiate a hyandoff)

• The signaling tone (ST)

– Is a 10Kbps data burst, which signal call termination by the subscriber.

– It is a special end-of call message consisting of ―1‖ and ―0‖, which is sent

on RVC by a mobile for 200 ms.

– Unlike blank and burst messages, which suspend the SAT transmission,

the ST tone has to be sent simultaneously with the SAT.

– ST alerts the base station that the subscriber has ended the call.

– When a user terminates a call, ST tone is automatically sent by the

mobile unit.

– This lets the BS and MSC know that a call was terminated voluntarily by

the user, as opposed to being dropped by the system



25

supervisory Audio tone (SAT)

• The purpose of SAT is indicate the continuity of the conversation

• A SAT is a high pitched, inaudible tone that helps the system distinguish between

callers on the same channel but in different cells. The mobile tunes to its assigned

channel and it looks for the right supervisory audio tone. Upon hearing it, the

mobile throws the tone back to the cell site on its reverse voice channel. We now

have a loop going between the cell site and the mobile phone. No SAT or the wrong

SAT means no good. And the call is dropped. The transmission of SAT in FVC and

RFC is called handshake. The handshake is required to dedicate a pair of FVC and

RVC to a call.



• AMPS generates the supervisory audio tone at three different frequencies. SAT 0 is

at 5970 Hz, SAT 1 is at6000 Hz, and SAT 2 is at 6030 Hz. Using different

frequencies makes sure that the mobile phone is using the right channel assignment.

It's not enough to get a tone on the right forward and reverse path -- the mobile

must connect to the right channel and the right SAT. Two steps. This tone is

transmitted continuously during a call. The tone is barely audible, and filtered out at

the receiver

• The mobile, in fact, drops a call after 1 second if it loses or has the wrong SAT.

The all digital GSM and PCS systems, by comparison, drops the call like AMPS

but then automatically tries to re-connect on another channel that may not be

suffering the same interference.

• The detection of SAT must be performed every 250 msecs by the subscriber units

• The dropped or prematurely terminated calls are often traced to incorrect detection

26

of SAT, or interference at the mobile

supervisory Audio tone (SAT) (Cont‘d)

• A given base station will always constantly transmit one of the 3 SAT tones on each

voice channel while it is in use

• The particular freq of a SAT denotes a particular base station location for a given

channel and is assigned by MSC for each call.

• A highly built up area may have as many as 3 cochannel base stations, in a small

geographic, the SAT enables the subscriber unit and base station to know which of

the three cochannel base stations is handling a call









27

supervisory Audio tone (SAT) (Cont‘d)









S2 S1 S0 S2

S1

S0 S2 S1

S1 S0 S2 S0



S2 S1 S2 S1 S0 S2 S1

S0 S2 S1 S0

Example of SAT assignment S1 S0 S2

Within a cluster of N=7





28

Blank and Burst Encoding

• AMPS Control and blank and burst channels transmit data at 10 Kbits (8

Kbps for ETACS)

• The data stream uses Manchester coding

– The advantage is that the energy is concentrated at 10 Khz, and a little energy

leaks into 4 Khz

– So burst of data over a voice channel can be easily detected within a 30 Khz RF

channel and barely audible to the user

– Can use phone lines which have DC blocking

• The coded data uses BCH block codes for FEC

– FVC /FCC uses (40, 28) BCH code

– RVC/RCC uses 48, 36) BCH code

• The data bursts are of the same length as the Block ( 40 or 48 bits)

• Uses FSK modulation with +-8 Khz deviation (+- 6.4 Khz for ETACS)

• Blank and burst is used to initiate a hanoff, change subscriber‘s Tx power

level, and provide other system data

• Allows MSC to send data on Voice channel by temporarliy suppressing

voice and SAT with data. Has to be less than 250 msecs.

– Barely noticable by a user







29

Voice Modulation and Demodulation









• Prior to frequency modulation voice signals are processed using a compander. At the

receiver these steps are reversed after demodulation.

Compander

– to accommodate a Large speech dynamic range, the input signals need to be

compressed in amplitude before modulation.

– 2: 1 compander which produces 1 db output change for a 2 db input change

– Nominal 1 Khz reference input tone at a nominal volume should produce +- 2.9

Khz peak freq deviation of the transmitted carrier.

– Companding confines the energy to the 30 Khz channel BW.

– At the receiver an inverse of compression is performed thus assuring the restoral

of the input signal

30

Example : Companding









A waveform before and after non-linear

companding (reduction of dynamic range)

31

Voice Modulation and Demodulation









• Pre-emphasis filter: The output of the compressor is passed thru Pre-Emphasis filter.

Which has nominal 6 db per octave response between 300 to 3000 Hz (This means

that as the frequency doubles, the amplitude increases 6 dB)

• Deviation limiter: This ensures that max freq deviation at the mobile is limited to +- 12

Khz (+- 10Khz fro ETACS) The supervisory signals and widebnad data are excluded

from this limitation

• Post deviation limiter filter: This is low pass filter. It has attenuation (relative to

response at 1 Khz ) which is gretaer than or equal to

– 40 log 10( F/3000) db for 3 Khz = 15 Khz the attenuation must be greater than 28 dB.

– This ensures that the restrictions on emission outside the band are met.

– Also makes sure that 6 Khz SAT tone (always present ) do not interfere with the

transmitted signal



32

Pre-Emphasis

• voice characteristics emit low frequencies higher in amplitude than high

frequencies. Higher energy in low frequencies.

• Pre emphasis is used to shape the voice signals to create a more equal

amplitude of lows and highs before their application to the limiter. The result

is that the signal received is perceived louder due to more equal clipping or

limiting of the signal, but probably more important is the increased level of

the higher frequencies being applied to the modulator results in a better

transmitted audio signal to noise ratio due to the highs being above the

noise as much or more than the lows

• The Preemphasizer emphasizes the high frequency components, because

they usually contain much less energy than lower frequency components,

even though they are still important for speech recognition. It is a high-pass

filter because it allows the high frequency components to "pass through",

while weakening or filtering out the low frequency components.

• The limiter circuits that clip the voice to allow protection of over deviation

are usually not frequency sensitive, and are fixed in level, so they will clip or

limit the lows before the highs.

• This results in added distortion because of the lows overdriving the limiter







33

Radio Interface









34

Narrow Band Advanced Mobile phone service

(NAMPS )

• NAMPS can service three MS in a 30 Khz bandwidth

• Uses 10 Khz channels and FDMA (increases the capacity of AMPS by a

factor of 3)

• In more congested areas, service providers could provide more trunked

radio channels hence increase cell capacity and provide a better GOS

• NAMPS also uses SAT, ST and blank and burst signaling just like AMPS,

but signaling was done in sub-audible band

• The max freq deviation is decreased, to reduce the signal BW, hence it

increase S/(N+I) ratio. To counteract that NAMPS uses companding to

provide synthetic voice channel quitening.

• NAMPS uses 200 Hz SAT and ST, and a 300 hz high pass band audio filter

is used

• SAT and ST signaling is sent using 200 bps NRZ, which is FSK modulated

• Since SAT and ST signals are sent repetetively in small predefined code

blocks (Called DSAT and DST) each 24 bits long

• There are 7 different 24 bit blocks DSAT codewords which may be selected

by MSC,

• A DSAT word is constantly repeated by MS and BS

• DST signal is binary complement of DSAT

• The 7 codewords specially deisgned to provide a sufficient number of

alternating ―1‖ and ―0‖ so that the code can pass thru even when DC

blocking implemented by the receivers 35

•

TDMA Vs AMPS

• The first generation AMPS was designed to support current demand for

capacity in large cities.

• Cellular systems that use digital modulation techniques, and digital signals

offer large improvement in capacity and performance

• The most commonly used digital cellular system in America is named IS-

54, also known as D-AMPS or digital AMPS. OR USDC, using the same

spectrum allocation as AMPS.

– (Interim Standard-54) The first generation of the TDMA digital cellular

system which was released in early 1991

• IS-54 uses a multiplexing technique called TDMA or time division multiple

access, in contrast to AMPS which uses FDMA

• The TDMA IS-54

– Supports three calls into the same 30kz channel space that AMPS uses to carry

one call.

– It does this by digitally slicing and dicing parts of each conversation into a

single data stream, We'll see how that works in a bit.

– Cellular systems might use both TDMA and FDMA like GSM or IS-136,

AT&T's latest digital cellular service.







36

TDMA

• All IS-54 mobile phones handle analog traffic as well as digital, a great

feature

– Allows travel to rural areas that don't have digital service and still make a

call.

– The beauty of mobile phones with an AMPS backup mode is they default to

analog.

– As long as the carrier maintains analog channels one can get through.

– this applies as well as to what's known as IS-95, a cellular system using

CDMA or code division multiple access. Your phone still operates in analog

if it can't get a CDMA channel.









37

Noth Americal standards

IS-136.2

AMPS and digital control

AMPS IS-54 B channel

EIA-553 USDC



IS-136.1

IS-136 introduces new features:

•A battery life power saving: called sleep mode DCCH

•Voice mail messaging wait indicator

•Support for multiple vocoders

•Support to seamlessly acquire service sin 800 (AMPS band ) and 1800 Mhz (PCS)

band

•Cellular messaging service

•Paging services

•A hierarichal macro, micro cell support







38

USDC (IS-54 and IS-136)

• IS-54 is the standard for the digital version of the US AMPS system.

• IS-54 has been replaced by the IS-136 standard.

• The system uses hybrid Frequency Division Multiple Access and Time

Division Multiple Access concept as it accepts 3 users per carrier.

• The carrier spacing 30 kHz, similar to the analog AMPS.

– Thus, assuming that the analog and digital system use the same

frequency reuse pattern, the digital version can accommodate three

times more users.

• In terms of frequency planning the digital system behaves similar to analog

AMPS.

• The USDC system was designed to use same frequency spectrum as

AMPS, freq reuse plan, and base station. If the subscriber equipment and

base station is eqiupped with both the AMPS channels and Digital channels

then the AMPS system can be migrated to USDC in a graceful manner

• Key requirement in transition from AMPS to TDMA was smooth transition

• IS-136: IS-136 added a number of features to the original IS-54

specification, including text messaging, circuit switched data (CSD), and an

improved compression protocol. SMS and CSD were both available as part

of the GSM protocol, and IS-136 implemented them in a nearly identical

fashion.





39

USDC (IS-54 and IS-136) Transition

Transition

• Since the AMPS and USDC uses same freq band, one can continue to provide

analog AMPS service, while introducing digital service. It can start offering digital

service to new customers.

• In rural areas sometimes only 666 of 832 channels are used. A provider may start

providing USDC service on extended channels, and provide USDC service to the

existing customers and roamers.

• In congested areas TDMA approach was introduced to increase the capacity

• Every time a channel is changed to TDMA, there is a temporary increase in

interference and dropped calls on the analog AMPS , since conversion to TDMA,

reduces the number of analog channels in a geographic area

• The changeover rate from AMPS to TDMA must carefully match the subscriber

equipment in the market

• To maintain the compatibility with AMPS USDC forward and reverse control channels

use exactly the same signaling technique as AMPS

• The USDC voice channels use p/4 DQPSK modulation with a channel rate of 48.6 Kbps,

but the signaling channels use 10 Kbps FSK as used in AMPS, and use the same frequencies

as AMPS

• As the system migrated to a complete digital systems, the control channels are also converted

to p/4 DQPSK modulation scheme and that is what is specified in IS-54 RevC (IS-136)



New services

• These control channels with p/4 DQPSK modulation with higher capacity could be used to

provide new services such as paging and short message service (SMS)

40

USDC Radio Interface

• To ensure smooth migration from AMPS to USDC the IS-136 is

specified to operate in a dual mode, which makes roaming possible

with a single phone

• USDC supports 3 subscribers in a single FVC/RVC channel

• USDC uses TDMA. as more efficient voice coding becomes

available, it could potentially support more subscribers









41

USDC Radio Interface









42

USDC Channels

Supervisory/control channel

– AMPS specifies 42 control channels ( 21 each for provider A and

provider B)

– IS-136 has specified additional 42 called secondary control channels

– The secondary control channels during transition can be allocated to

USDC only, so AMPS does not have to monitor or decode these

channels, and the SMS and paging services may be introduced for

USDC only

– After the transition is complete all the control channels will be used, to

carry the signaling, paging and SMS traffic

• Voice channels: Same as AMPS except converted to TDMA. Occupies 30

Khz bandwidth in forward as well as in reverse direction. Each Voice channel

supports a max of 3 users, and has six time slots.

– For full rate speech coding a max of 3 users

– For half rate speech coding a max of 6 users

– User 1, may occupy slots 1 and 4, user 2 may occupy 3 and 5 slots,

while user 3 may occupy 3 and 6 time slots

– A half rate user occupies only one slot





43

USDC Frame and Slot Format

s2

Tx F1: Reverse channel TX



S1 s3 s4 s5 s6







S1 s2 s3 s4 s5 s6







44

Forward f1+45 Mhz

Sym Receive

bols



SACCH: Slow Associated control channel

CDVCC:Coded digital Verification Color

code (12 bits): similar in functionality to

SAT in AMPS

TS 1, 4, TS2, 5 and TS 3 , 6 make up one

voice channel







44

USDC Frame and Slot Format



• The time slots in the forward and reverse channels are staggered in

time so that the time slot 1 of the nth frame in the forward channel

starts exactly one time slot plus 44 symbols after the beginning of

the time slot 1 of the nth frame on the reverse channel.

• This allows each mobile to simply use a transmit and receive switch

rather than a duplexer operation within the reverse and forward link

• USDC has the ability to adjust the time stagger between forward and

reverse channel time slots in integer increments of a half a time slot,

so that the systems may synchronize new subscribers that are

assigned a time slot

One slot 324 Bits

one frame 1944 bits

Frame Duration 40 Msecs

Frame per sec 25

Speed 48.6 Kbps

Slot duration 40/6=6.667 msecs.

45

Reverse Slot Format

6 6 16 28 122 12 12 122

CVDCC

G R Data synch data SACCH Equ to Data

SAT

40 Msecs

Reverse Voice Channel slot format

Supervisory channels

• Coded digital Verification Color code (12 bits): similar in functionality to SAT in AMPS. CVDCC is

an 8 bit number which is protected by additional 4 bits using Shortened Hamming code.

– Base station sends this info to a mobile in the forward slot. The subscriber must receive,

decode, and retransmit it back. Any time this code is not received correctly (both at mobile

and base station) the slot will be released and the subscriber TX will be turned off

automatically.

– Transponding of the code is called handshake

• Slow Associated control channel (12 bits)

– Transmitted In every forward and reverse slot.

– Single message in many consecutive slots

– Communicates power level changes, and handoff information

– Mobile reports the results of signal strength measurements of its and neighboring base

stations, so that the base station may implement Mobile assisted handoff

• Fast Associated control channel (FACCH): Used for important and urgent messages from the

base to subscriber

– Takes the place of user information data within the slot

– Similar to blank and burst

– Supports transmission of DTMF data from touch tone keypads, call release and flash hook

instructions

– When the slots not in use, FACCH can carry other internal data within the network

– FACCH is treated the same way as speech

– Use rate ¼ convolution coding for protection

46

Reverse Slot Format

6 6 16 28 122 12 12 122



G R Data synch data SACCH CVDCC Data



Reverse Voice Channel slot format

324 Bits in a slot in 40 milli-secs frame

• The data channel consists of 3 data portions: one carries 16 bits,

and the other 2 carry 122 bits of data each for a total of 260 bits

– Each time slot carries interleaved data from two adjacent frames of

the speech coder. A frame of speech coder is 20 msecs long, which

is half the length of the TDMA frame.

– Each 20 msec frame of speech data is actually 159 bits, but channel

coding brings the bits to 260 bits per 20 msecs.

– 2 speech frames are interleaved for further protection

• The guard and Ramp bits are 12 bits long

– guard time, the period between each time slot . The guard time

protects the time slot being received outside the time slot due to

propagation delay between a mobile and a base station

– R: ramp time has a 6-bit ramp time to enable its transmitter, time to

get up to full power

• Synch is 28 bits long

47

Forward Slot Format

28 12 130 12 130 12

synch SACCH data CVDCC Data Reserved







• Synch: 28 bits

– USED for synchronization, and they contain a specific bit sequence known by all receivers

to establish frame alignment. Also, as with GSM, the known sequence acts as a training

pattern to initialize an adaptive equalizer.

– The equalizer r adjusts the receiver to compensate for radio channel distortion

– The IS-54 system has different synchronization sequences for each of the six time slots

making up the frame, thereby allowing each receiver to synchronize to its own preassigned

time slots.

• SACCH: Slow Associated control channel (12 bits)

– Transmitted In every forward and reverse slot.

– Single message in many consecutive slots

– Communicates power level changes, and handoff information

– SACCH does not perform handoffs but conveys things like signal strength information to the

base station.



• Data ; 2 130 bits allocations for a total of 260 bits, from two consecutive

interleaved speech frames.

– Each time slot carries 324 bits of information, of which 260 bits are for the 13-

kbit/s full-rate traffic data

48

Forward Slot Format (cont‘d)



28 12 130 12 130 12



synch SACCH data CVDCC Data Reserved







• Coded digital Verification Color code (12 bits): similar in functionality to SAT in AMPS.

CVDCC is an 8 bit number which is protected by additional 4 bits using Shortened

Hamming code.

– Base station sends this info to a mobile in the forward slot. The subscriber must

receive, decode, and retransmit it back. Any time this code is not received

correctly (both at mobile and base station) the slot will be released and the

subscriber TX will be turned off automatically.

– A total of 256 color codes

– Each base station has its own preassigned color code, so any incoming

interfering signals from distant cells can be ignored.

– A unique CVDCC per cell ensures that the correct mobile is talking to right base

station





• In IS136out of 12 reserved bits, 11 bits are used for Coded digital locator

which indicates a range of 8 RF channels where DCCH is found 49

– Allows the mobile to find DCCH during an initial scan

Full rate Voice channels

• A full rate traffic channel uses 2 time slots

• A mobile typically uses idle time to measure the signal

strength of the surrounding channels to assist in MAHO









50

Speech Coding

• Speech coding: Vector Sum Excited Linear Prediction (VSELP)

– special type of speech coder within a large class known as code-excited

linear prediction (CELP) coders

• Based on codebooks which determine how to quantize the residual

excitation signal

• The VSELP uses a code book with a predefined structure, such that

the number of computations required for code book search process

is optimized.

• Developed by consortium of companies

• Motorolla implementation was chosen for IS-54 standard

• Output bit rate of 7940 Bps, and a speech frame every 20 ms.

• In one frame there are 7940*20*10-3 = 159 bits of speech









51

Speech compression

64 Kbps Digital 7.950 Kbps

Analog Voice

A/D converter Sig

Processor







Sig analysis Codebook

program tables



Error

Protection

coding









52

Channel Coding

For Speech

• 159 speech bits in a 20 msec frame (7.95 *20 = 159 bits)

– 77 class 1 bits (have more perceptual significance as compared to class

2 bits

• 12 bits: more significant class 1 bits

• 65 bits

– 82 class 2 bits

• Class 1, 12 more significant bits are error protected using 7 bit CRC error

detection code

• Thus (19+ 65 ) bits along with 5 tail bits use half rate convolution code of

constraint length k=6 for error protection, producing 178 bits= (19+65+5)*2

• The class 2, bits are not error protected.

• Thus total number of bits per 20 msec frame are 178+82 = 260 bits

• The five tail bits are used to bring the state of convolution coder to ―0‖ state,

before it codes next stream.









53

Error protection for a speech frame









54

Channel Coding

Fast associated control channel (FACCH)

• A FACCH data block = 49 bits per 20 msecs

• A FACCH data block after 16 bit CRC protection = 65 bits

• Uses quarter rate (1/4) convolution coder with constraint length of 6,

producing 65*4 = 260 bits per slot

• FACCH data block is as long as a single data frame of speech

• So FACCH data block replaces speech code when required

• Interleaving of FACCH and speech data is identical

SACCH

• SACCH data word = 6 bits during each 20 ms speech frame

• Uses half rate convolution coder with constraint length of 5,

producing 6*2 = 12 bits per slot- 20 msecs of speech







55

Inter-leaving

Interleaving for speech

• Before TX, the encoded speech data is interleaved over 2 time slots with the

speech data from adjacent speech frames.

• Speech data is passed thru a rectangular interleaver 0f 26*10 inter-leaver.

• The data is entered into the columns of the interleaving array.

• Two consecutive speech frames are refered to x and y. where x is the previous

speech frame.

• It is seen that only 130 of the frame bits are provided for both x and y frames.

• The encoded speech data for the 2 adjacent frames are placed into the interleaver

in such away so that it intermixes class 1 and class 2 bits.

• Speech data is transmitted row wise

Interleaving for coded FACCH

• Identical to speech

Interleaving for coded SACCH

• 6 bit SACCH message Uses half rate convolution coder with constraint length of 5,

producing 12 bits

• Uses incremental intreleaver which uses 12 consecutive time slots









56

Interleaving 26*10



Two(2)

20msecs

Speech

rames are

nterleaved.

Half the data

carried in first

ime slot,

another half in

second time

slot)



57

Modulation

• 48.6 Kbps per 30 Khz channel

• BW efficiency requirements are = 48.6/30 = 1.62 bits per hertz.

• Spectral shaping to limit adjacent channel interference

 p /4 DQPSK is used , with channel symbol rate of 24.3 symbols per sec.

• Pulse shaping: Square root raised cosine filter with a roll off factor of

0.35 is used to reduce inter-symbol interference

• The receiver will employ a corresponding filter

• After pulse shaping is applied, it is no longer non-linear, but linear

modulation scheme.

• Thus linear amplification is required to maintain the pulse shaping

• Provides adjacent channel protection of 50 dbs









58

Demodulation



• Type of demodulation left to the implementer

– At IF or at Baseband

– At baseband, one may use a simple discriminator, or DSP

– Reduces the cost but simplifies the RF circuitry also

– DSP support equalization and dual mode support









59

Equalization

• Measurements in 900 Mhz band indicated that

– Rms delay spreas are less than 15 ms at 99 % of all locations in four US

cities

– Less than 5 ms for nearly 80 % of all locations

• For a system using DQPSK modulation at a symbol rate of 24.3

symbols per sec,

– if BER due to inter-symbol interference becomes intolerable for s/T =0.1

(where s is rms delay and T is the symbol duration)

– Then the max valus of of rms delay spread is 4.12 ms.

• If the max rms delay spread exceeds 4.12 ms. Then equalization

must be used to reduce BER

• It has been shown in technical literature that rms delay spreda

exceeds 4 ms. At about 25 5 of the locations in four cities , so the

equalizer was specified for USDC, but specific equalizer

implementation not specified in the standard







60

USDC Derivatives

• IS-94 and IS-136

– Because of digital technology, additional networking features were provided,

which led to new types of wireless services

– TDMA provides MAHO capability, mobiles are able to monitor channel

conditions and report those to the base station, allowing greater flexibility

• As an example MAHO can be used to support dynamic channel

allocations, carried out by base stations

• This allows an MSC to use a larger number of base stations located at

strategic places throughout the service area, and provides each base

station with greater control over its coverage area.

– IS-94 enabled cellular phones to interface directly with PBXs.

– By moving intelligence closely to a base station, it becomes possible to provide

wireless PBX services in a building or a campus, while using small base

stations that can be placed in closets thoughout the building.

– IS-94 specifies a way to provide private or close user group that uses non-

standard control channel.

• IS-136 specifies capabilities which makes it competitive with IS-95 (CDMA) and

GSM 2G standards

– Specifies SMS

– user group features

– Allowing wireless PBX services and paging services to be provisioned.

– IS-136 uses 48.3 DQPSK modems on all control channels ( not 10 Kbps FSK ),

thus making modems more cost effective



61

Additional info



Refernces







http://www.privateline.com/Cellbasics/hart-ch3IS-136.pdf

http://www.iec.org/online/tutorials/acrobat/pcs.pdf 62

Dynamic time allignment

IS-54 variant IS-94 and IS-136

IS-136 uses existing radio spectrum in 850 Mhz band and PCS

spectrum in 1900 Mhz band

Superframe = 16*40 =640 ms

Hyperfarme = 2 superfarems = 2*640 =1.28 secs.









63

• IS-54B uses Vector sum excited linear

predictive coding (VSELP) fro speech

compression

• IS-136 additionlly can use Enhanced full

rate (EFR) algebraic code excited linear

predictive coding (ACELP)







64

Time alignment

Forward link format



• F-BCCH; Forward link: The info that MS needs immidiately for system

identification and registration info.

• E-BCCH; information that is not required immediately such as neighbor

base station listlist

• System uses short message service, paging and access response channel

to a particular phone









65

Time alignment

Reverse link format DCCH





6 6 16 28 122 24 122

122

G R Preamble synch Synch+ 122

data



Normal Reverse Digital control channel (DCCH) slot format

324 Bits



6 6 16 28 122 24 78 6 38

122 78

Normal Reverse Digital control channel (DCCH) slot format

G R Preamble synch

data

324 Bits

Synch+

Data R AG



DCCH abbreviated uplink format= 324



AG: Additional guard band for randon access channel









66

Time alignment

Forward link format

DCCH



28 12 130 12 130 10 2

CVDCC

synch SCF data Data SCF RSVD

CSFP



DCCH Downlink burst format

CVDCC is replaced by frame counting field, called

coded superfarme phase

SACCH replaced by Shared channel feedback. This

field is a collection of flags used as a method of

control and ack for the info sent from the base to

mobile

The voice field data is replaced by DCCH data

67

Superframes and hyperframes





• Superframes and Hyperframes are used to multiplex logical groups

of data togetehr and to provide a known repeatable sequence on

the airinterface.

– Allows a mobile to retreive info quickly and to develpe sleep mode in

which a mobile needs to wake up at predefined instances to receive

messages









Only slot 1 and 4 carry DCCH in a superframe. That

is in a SF, there are 32 DCCH bursts, spread over a 68

total of 96 bursts

DCCH









DCCH:: digital control Channel

BCCH: Broadcast control channel

SPACH: SMS pt to pt messaging,

paging, and access response channel

MS



Paging up to 7 channels (W1 to W7)

Variable bit rate user info

Traffic Channels (exceptW32,W0) Power control 800 bps



Signaling messages









175

Forward Traffic Channel (TCH)

• Forward Traffic Channel (FTC)

– Supports variable user data rates

• 9.6, 4.8, 2.4 and 1.2 Kbps (Rate set 1)

• The modulation process in the figure on next page

• Speech data rate applied to the transmitter is variable over the

range 1.2 to 9.6 kbps

– FTCH always continuously transmits power control subchannel

– A ―0‖ in a specifies bit specifies that the mobile increase it‘s TX powwer by 1 db,

– A ―1‖ in a specifies bit specifies that the mobile decrease it‘s TX powwer by 1 db,

– Power control bits puncture the modulated data symbols at a rate of 800 bps. A

single power control bit replaces 2 data symbols.







http://www.sss-mag.com/pdf/cdmaover.pdf









176

Forward CDMA Channel Modulation





Symbol repetition





19.2

64:1 24:1





/4 on second decimator: removes first four bits in each 1.25 ms interval

Power contro bit = 1 bit in 1.25 msecs

Bits /sec = 1000/1.25 = 800 . The 19.2 kbps long code is decimated to 800 bps ( The first PN chip of

every 24 chips)







1. Data is grouped into 20 ms frames.

2. User data is first convolutionally coded, formatted and interleaved to

adjust actual user rate, which may vary

3. Then the signal is scrambled using a long PN sequence at a rate of

1.2288 Mcps, and then spread using Walsh code

4. The decimator : The first PN chip of every 64 chips coming out of the long

code generator provided by the decimator is used for data scrambling

(Modulo 2 addition) 177

Forward Traffic channel modulation









178

Forward Modulation process: Convolution Encoder

and Repetition Circuit

• Speech and data are encoded using

– Half rate convolution coder, with constraint length of 9

– The encoding process is described by generator vectors G0, and

G1, which are 753 and 561 octal respectively

• The speech encoder uses voice activity detection, and reduces its

output from 9.6 to 1.2 Kbps during silent periods

– In order to keep a constant baseband symbol rate of 19.2 kbps,

for user data rates of less than or equal to 9.6 Kbps, each

symbol from the coder is repeated, before interleaving

• Number of repetitions after convolution encoder



Data rate. Number of repetitions

9.6 Kbps 1

4.8 2

2.4 4

1.2 8



• Repetitions result in a constant data rate of 19.2 kbps

179

Modulation process Forward Channel (Cont‘d)

• Intreleaver

– The symbols are sent to a 20 ms (19.2 *20 =384 bits) inter-leaver, which is a 24

*16 array. The interleaver writes the code symbols into the matrix on a column-by-

column basis for all of the input data symbols and reads the stored data into the

output buffer in accordance with the IS-95A specification

• Long PN sequence

– A direct sequence is used for data scrambling

– A long periodic sequence is uniquely assigned to each user, with a period of

242-1 chips.

– Corresponds to a repetition of one per century

– Long code is specified by the following characteristic polynomial

– X42 + x35 +x33 + x31 + x 27 + x 26+x 25 + x22 + x21 + x19 + x 18 + x17 + x16 +

x10 + x 7 + x6 + x 5+ x 3+ x 2 + x 1 + 1



– Each PN chip is generated by modulo 2 inner product of a 42 bit mask and the 42

bit state vector of the sequence generator.

– Initial state of the generator is defined to be when the output of the generator

becomes ‗1‖ after following 41 consecutive ―0‖ outputs, with a binary mask

consisting of one ―1‖ in the MSB followed by 41 zeros

– 2 types of masks are used

• A public mask for mobile station‘s ESN, and a private mask for Mobile‘s

station ID number (MIN)

– All mobile calls are initiated using the public mask

– Transition to private mask is carried out after authentication is completed. 180

Modulation process Forward Channel (Cont‘d)

Masks

• Public long code is as follows:

– M41 to M32 is set as 1100011000 (10bits)

– M31 to M0 is set as the permutation of mobile‘s ESN (32 bits)

– ESN = (E31,E30,E29, E28, E27, ………. E3, E2, E1, E0)

– Permuted ESN ( E0, E31, E22, E13, E4, E26, E17, E8, E30, E21, E12,

E3, E25, E16, E7, E29, E20, E11, E2, E24, E15, E6, E28, E19, E10, E1,

E23, E14, E5, E27, E18, E9)

• Private long code is specified as follows:

• M41, M40 are set as ―01‖

• M39 to M0 are set by a private procedure









181

Public and Private long code mask









182

Modulation process Forward Channel (Cont‘d)

Data Scrambler



• Data Scrambling after block interleaving

– The 1.2288 Mhz PN seq is applied to a

decimeter, which keeps only the first chip out

of every 64 consecutive PN chips

– The symbol rate from the decimator is 19.2

kbps

– The scrambling is performed by modulo 2

addition of the interleaver output with the

decimator output symbol



183

Modulation process Forward Channel (Cont‘d)

Power Control sub- channel

• IS-95 strives to maintain the received power at a base

station to be same for each user, in order to minimize Av

BER

• The base station reverse Traffic channel receiver

estimates and responds to a signal strength for a given

mobile

• Signal and interference are continually varying, power

control updates are sent by the base station every 1.25

ms

• Power control instructions sent to every mobile to

– Raise or lower mobile Tx power in steps of 1 dB

• If received signal is low, a ―0‖ is transmitted over the

power control subchannel, for increasing its mean output

power level

• If received signal is high, a ―1‖ is transmitted over the

power control subchannel, for decreasing its mean 184

output power level

Modulation process Forward Channel (Cont‘d)

Power Control sub- channel

• Power control bit corresponds to 2 modulation symbols on the FTC

(1.25 msec), and are inserted after data scrambling

• During a 1.25 ms, (19.2*1.25ms) 24 data symbols are transmitted,

IS-95 specifies 16 possible power control group positions for the

power control bit.

– Each position corresponds to one of the first 16 modulation

symbols

– 24 bits from long code decimator are used for data scrambling in

1.25 ms period.

– The last 4 bits (23, 22, 21 and 20 ) are used to determine the

position of the power control bit.

– In the example last four bits are 1011 ( 11 decimal) , thus power

control bit starts in 11 position









185

Power Control Bits: Randomization

1 power bit in 1.25 ms

20*800=16 power bits

in 20msec frame

# of symbols in 1.25 msec

= 1.25*19.2= 24 symbols









186

Modulation process Forward Channel (Cont‘d)

Orthogonal covering



• Each TCH after the data scrambling, is spread with a Walsh function

at a fixed chip rate of 1.2288 Mcps

• Walsh code consists of 64 binary sequences, each of length 64 ,

which are orthogonal to each other

• A user that is spread using Walsh function n is assigned channel

number n

• Walsh seq repeats every 52.083 ms, equal to one coded data

symbol (1/19200)

– In other words each data symbol is spread by 64 Walsh chips

• 64 by 64 Walsh function matrix (HADAMARD matrix) is

generated as follows





187

Modulation process Forward Channel (Cont‘d)

generation of Walsh Function

• H1 = 0 H2 = 0 0

0 1

H2N = HN HN

0 000

HN HNc N is power of 2

0 101 HNc is the 2‘s

H4 =

0 011 complement

0 1 10

Each row in 64 by 64 Walsh function corresponds to the row number. For

channel number n, the symbols are spread by 64 Walsh chips in the nth

row. Channel number ―0‖ is always assigned to Pilot channel

Channel ―0‖ represents Walsh code ―0‖, which is all ―0‖

(1) The pilot channel is thus nothing more than a blank code and thus

consists of quadrature PN spreading code.

(2) The synch channel is assigned channel number 32

(3) If paging channels are present , they are assigned lower code channel

numbers

(4) All other channels are Traffic channels 188

Modulation process Forward Channel (Cont‘d)

Quadrature Modulation

• After orthogonal covering, signals are spread in quadrature

• A short binary spreading sequence with a period of 215-1 chips is used for acquisition and

synchronization at each mobile receiver and is used for modulation

• This seq is called Pilot PN seq and is based on the following characteristics polynomials

PI (x) = x 15+ x 13 + x9 + x 8 + x 7 + x 5 +1 for in phase modulation

PQ (x) = x 15+ x 12 + x11 + x10 + x 6 + x 5 + x 4 + x 3 + x2 1 for quadrature

modulation

• Based on the polynomial the pilot PN seqs i(n) and q(n) are generated by the linear recursions









i(n) = i(n-15) + i(n-10)+ i(n-8)+i(n-7)+i(n-6)+ i(n-2)



q(n) = q(n-15) + q(n-13) + q(n-11) + q(n-10)+ q(n-9)+ q(n-5)+

q(n-4) + q(n-3)

A ―0‖ is inserted in each sequence after the contiguous 14 ―0‖s To generate pilot PN seq of

length 215.

Initial state of both I and Q pilot PN seq is defined as the state in which the output of the pilot

PN seq generator is the first ‗1‖ output after following 15 consecutive ―0‖ outputs. The chip

rate for pilot seqs are 1.2288 Mbps. 189

Modulation process Forward Channel (Cont‘d)

Quadrature Modulation









The binary I and Q outputs of the quadrature spreading are

mapped in to phase as shown in the table.





190

Reverse CDMA Channel

• User Data is grouped into 20 ms frames.

• User data is first convolutionally encoded, block interleaved, , modulated

by 64-ary orthogonal modulation, and spread prior to modulation

• Table shows modulation parameters

• The speech and data rates supported are 9.6, 4.8, 2.4 and 1.2 Kbps

• The reverse channel comprises of

– Access channel

• Fixed data rate of 4.8 Kbps

• Used by mobile to initiate communications with the base station,

and respond to the pages

• A random access channel, each user identified by their long

codes

– Reverse Traffic Channel (RTC): variable data rate of 9.6. 4.8. 2.4 and

1.2 Kbps

• Access and RTC share the same freq assignment and are identified by

distinct user long code.

• The reverse channel may contain up to 32 ACs per supported paging

channel





191

Reverse CDMA Channel (Cont‘d)





Access (up to 32 channels 4.8 Kbps)



reverse

Variable bit rate user info







Signaling messages









192

Access Channel (MS-BS)

• Registration messages; location, status, identification,

and other parameters for registration

• Call initiation message: sending dialed digits etc

• Page response message: for call termination etc

• Authentication messages: Mobile ID validation etc









193

Reverse CDMA Channel (Cont‘d)

Modulation Process









28.8

Kbps









Chip duration = 1/Chip rate

User data grouped in 20 msecs

Bit rate repetition

Bits per symbol in walsh symbol =6

9.6 Kbps 1

# of walsh symbols = 28.8/6 =4.8 Ksps

4.8 kbps 2

Walsh chip rate = 4.8*64 = 307.2 Kcps

2.4 4

I PN chip = 813.8 ns

1.2 8

½ PN chip delay = 406.9 ns

194

Reverse CDMA Channel (Cont‘d)

Modulation Parameters









195

Reverse CDMA Channel (Cont‘d)

Convolution Encoder and Symbol Repetition



• A Subscriber‘s data is encoded using 1/3 rate convolution coding, with

constraint length of 9

• The three generator vectors g0, g1, and g2 are 557 (octal), 663 (octal), and

771 (octal) respectively

• Coded bits are repeated before interleaving when data rate is less than 9.6

Kbps

• Identical to forward channel.

• After repetition the symbol rate is 28.8 Kbps



Block Interleaver

• Performed after Convolution coding

• Block interleaver spans 20 ms. ( 576 bits)

• An array of 32 rows and 18 coloums

• Code symbols are written by columns but read by row





196

Reverse CDMA Channel (Cont‘d)

Orthogonal Modulation

• M-ary Walsh modulation, where M = 2W and W is the Walsh order

parameter. For 64-array orthogonal modulation M=64 = 26. W=6

• 28.8 kbps is converted to 6 bit symbols

– Symbol rate = 28.8/6 = 4.8 Symbols/sec

– For every 6 input bits, the block generates one of the Walsh symbols from a set of 2W Walsh

sequences.

• A 64-ary orthogonal modulation

• One of 64 possible Walsh functions is transmitted for each group of 6 coded

bits

• 64 Walsh chips are transmitted within a Walsh function.

• The selection of a Walsh function is as follows:

– Walsh Function Number = c0 + 2 c1+ 4 c2+8 c3 + 16 c4 + 32 c5

– c5 represents the last coded bit and c0 the first coded bit of each group

of 6 coded symbols (c5,c4,c3,c2,c1,c0) is a 6 bit code number

• Walsh chips transmitted at a rate of 307.2 Kbps

– 28.8 Kbps * (64 Walsh chips)/(6 Coded bits) = 307.2 chips per second

• Walsh functions in reverse channel are used for data modulation, where as

in forward channel, the Walsh functions are used for spreading to denote a

particular user channel



197

Reverse CDMA Channel (Cont‘d)

Data Burst Randomizer

• Data Burst Randomizer takes advantage of voice activity on the reverse

channel.

– It is used to reduce reverse link power during a quite period of speech by

pseudorandom masking out redundant symbols produced by symbol repetition.

– The data burst randomizer generates a masking pattern of ―1‖s and zero‘s to

randomly mask out the redundant data.

– The masking pattern depends on Vocoder rate ( data rate).









198

Reverse CDMA Channel (Cont‘d)

Variable data rate

• Variable data rate 9.6, 4.8.2.4 and 1.2 Kbps

• Code symbol repetition introduces redundancy for data rates less than 9.6

kbps.

• A data randomizer is used to transmit certain bits while turning the

transmitter off at other times.

• For data rates of 9.6 Kbps, all interleaver output bits are transmitted

• When the data rate is 4.8 Kbps, half of the interleaver bits are transmitted,

and the mobile unit does not transmit 50 % of the time.

• Data in each 20 ms frame are divided into 16 power control groups, each

with a period of 20/16 = 1.25 ms.

• Some power control groups are gated on, while some are gated off.

• Data burst randomizer ensures that every repeated code symbol is

transmitted exactly once.

• During gate off the mobile transmitter reduces its EIRP by 20 dB with

respect to most recent gated on period, or to noise floor which is greater

• This reduces interference to other mobile stations operating on the same

reverse channel.



199

Reverse CDMA Channel (Cont‘d)

Data burst Randomizer



• Data burst Randomizer generates a masking pattern of ―0‖ and ―1‖

that randomly masks the redundant data generated by the code

repetition process.

• A block of 14 bits taken from the long code determines the masking

pattern.

• The last 14 bits of the long code used for spreading in the second to

last power control group (15 th power control group out of 16) of the

previous frame are used to determine the mask for the gating.

These 14 bits are denoted by

• b0 b1, b2, b3, b4, b5, b6. b7, b8, b9, b10, b11, b12, b13

• Where b0 represents the earliest bit and b13 the last bit









200

Reverse CDMA Channel (Cont‘d)

Data TX Algorithm

• If the user data rate = 9.6 kbps, the tx occurs on all sixteen power

control groups

• If the user data rate is 4.8 kbps the transmission occurs on 8 power

control groups as

– b0, 2+b1, 4+b2, 6+b3, 8+b4, 10+b5, 12+b6, 14+b7

• If the user data rate is 2.4 kbps the transmission occurs on 4 power

control groups numbered

• 1) b0, if b8=0, or 2+b1, if b8=0

• 2) 4+b2, if b9=0, or 6+b3 if b9=1

• 3) 8+b4, if b10=0, or 10+b5 if b10=1

• 4) 12+b6, if b11=0, or 14+b7 if b11=1







201

Reverse CDMA Channel (Cont‘d)

Data TX Algorithm

• If the user data rate = 1.2 kbps, the tx occurs on two power control

groups numbered;

• 1) b0, if (b8 =1, and b12 =0), or 2+b1 if(b8=1, and b12 =0) or

4+b2 if (b9=0 and b12=1) or 6+b3 if (b9=1, and b12=1)

• 2) 8+b4 if (b10=0 and b13=0) or 10+b5 if (b10=1, and b13=0) or

12+b6 if (b11=0 and b13=1) or 14+b7 if (b11=1, and b13=1)









202

Reverse CDMA Channel (Cont‘d)

Direct sequence spreading

• Reverse traffic channel is spread using long PN sequence which

operates at a rate of 1.2288 Mcps

• The long code is generated the same way as in forward traffic

channel

• Each Walsh chip is spread by four long code PN chips









203

Reverse CDMA Channel (Cont‘d)

Quadrature Modulation

• Prior to transmission the RTCH is spread by I and Q channel

pilot PN sequences.

– Identical to those used in forward CDMA channel process

– Pilot sequences used for synchronization.

• The reverse link modulation is offset QOSK

– The data spread by Q pilot PN seq is spread (406.901ns) by half a

chip, wrt to I pilot PN seq data spread .

– This delay is used for improved spectral shaping and

synchronization

– The binary I and Q are mapped into the phase as follows



I Q Phase

0 0 p/4

1 0 3 p/4

1 1 -3 p/4

0 1 - p/4 204

IS-95, 14.4Kbps Speech Coder

• To support Higher data rate for better speech quality, the IS-95 air interface structure

has been modified to accommodate higher data rate services for PCS

• For the reverse link the convolution code rate is changed from 1/3 to ½

• For the forward link the convolution code rate is changed from 1/2 to ¾ by puncturing

2 of every 6 symbols from the original rate ½ encoded symbol stream.

• These changes increase the effective info data rates from 9.6, 4.8, 2.4 and 1.2 Kbps

to 14.4, 7.2, 3.6 and 1.8 Kbps, while keeping the remaining air interface unchanged.

• A variable rate speech coder QCELP13 is designed to operate over this higher data

rate channel. This provides several other improvements

– Spectral quantization

– Improved voice activity detection

– Improved pitch prediction, and pitch post filtering

• QCELP13 codes the speech signal at the highest data rate when active speech is

present, and the lowest data rate when idle

– Intermediate data rates are used for different modes of speech, such as stationary voiced

and un-voiced frames

– Thereby reducing the average data rate and thus increasing system capacity









205

Reverse CDMA Channel (Cont‘d)

Variable Data Rate









206

Forward looking areas

Research

Architecture Research

• next-generation network architecture for wireless mobile telecommunications networks, including IP

Multi-media Subsystem.

• QoS

• Bridging non-IP, existing wireless networks, with IP architecture

• Mobility management and solutions ( both for IP and non-IP devices)

• Universal roaming (anytime, anywhere services)

• Wireless Intelligent services

• Integrating Pico/micro/macro cells

– LAN/WAN/ satellite services

• Adhoc networking: Mesh networks in mobile environment

– Defense applications, and disaster recovery



Antennas

• Smart antennas: beam forming antennas where the beam adaptively (i.e. smartly) tracks the

receiver (i.e. the mobile phone) as the person carrying it moved around, just like the beam from a

flashlight can be used to track a person moving in the dark

– Achieved by combining the processing technology with antenna arrays

• Multiple In Multiple out: Multiple-input multiple-output, or MIMO, is an abstract mathematical

model for multi-antenna communication systems where the transmitter has multiple antennas

capable of transmitting independent signals and the receiver is equipped with multiple receive

antennas

– Each RF chain and its corresponding antenna are responsible for transmitting a spatial stream.

A single frame can be broken up and

– multiplexed across multiple spatial streams, which are reassembled at the receiver.





207

Forward looking areas (cont‘d)

Research

• Modulation/FEC techniques

– Improving the spectral efficiency

– SSB again being looked at.

• Battery

– Enhancement in battery life

• Turning mobile off to extend the battery life.

• Looking at ways of elongating the battery life when not transmiting

– Sleep mode etc.

• Digital processing

– More efficient Vocoding techniques

– Compression techniques etc.

• Security









208

Cordless Telephony









209

Cordless Telephony

• DECT, PACS, and PHS are three well-known

International standards for low-mobility low-

power wireless communication applications.

• These standards have been developed for

operation in microcellular environments with

small cells typically several hundred meters in

diameter.

• However, with fixed elevated antennas at

subscriber locations, and other enhancements

and modifications, the range can be extended to

several kilometers, making them suitable for

WLL applications in sparsely populated areas.

210

CT2 Standard for Cordless telephones

• 2nd generation cordless system introduced in GB in 1989

• Used in both office and domestic environment

– Within residential a single base station provides voice and data support, enabling

in-house communication, as well as connectivity to PSTN

– Office: A small office supported by a single base station, providing service to a

number of handsets and data devices. In a large office multiple base stations can

be used in a cellular configurations, with the base stations connected to PBX.

• Allows a subscriber to use a CT2 handset at a pubic telepoint ( A public telephone

booth or a lamp post to access PSTN)

• Provides telepoint service

CT2 Services and features

• Compact telephone with built in antenna

• Digital version of analog cordless teelphone

• Provides better speech quality (compared to analog CT)

• More resistance to noise, interference and fading

• Provides better sceurity

• Calls are made after entering a PIN (personal ID Number)

• Battery : typical talk time of 3 hrs, and a standby time of 40 hrs.

• Uses dynamic channel assignment , minimizing system planning, and organization

within a crowded office or urban environment







211

CT2 Standard

• Defines how a cordless fixed part (equivalent to base station) and

cordless portable part (equivalent to subscriber station

communicate over a radio link

• The allocated freq in Europe and Hong kong are 864.1 to 868.1

Mhz, with 40 TDD channels, each with 100 Khz bandwidth

• CT2 defines 3 air interface signaling layers, and speech coding

techniques

– Layer 1 defines TDD, data muxing, and link initiation and handshaking

– Layer 2 defines data acknowledgement, error detection, and link

maintenance

– Layer 3 defines protocol used to connect CT2 o the PSTN









212

CT2 Radio Specs summary









213

CT2 Standard (cont‘d)

Modulation:

• all channels use Gaussian filtered binary FSK, with bit transitions constrained to be

continuous.

• The commonly used BT = 0.3 for the Gaussian filter

• Peak freq deviation is 25.2 Khz for all possible data patterns

• Channel TX rate is 72 kbps

Speech Coding

• Uses ADPCM with a bit arte of 32 Kbps

• Complies with CCITT standard G.721

Duplexing

• Uses TDD, with a frame duration of 2 msecs. Eqaully divided into reverse and forward

channel

• 32 Kbps digitized speech is transmitted at 64 Kbps.

• Each 2 msec worth of speech is transmitted in 1 msec, with 1 msec gap used for

return path.

• Eliminates the need for a paired frequency channel, or a duplex filter in the subscriber

unit.

• Since each CT2 channel supports 72 Kbps, the remaining 8 kbps is used for control

data and burst syncronization.

• Channel BW may be allocated to oe or more of the subchannels

– Different possible sub-channel combinations are called multiplexes

– Three different mulitplexes may be used in CT2

• Range 214

– Range is up to around 200 meters from the nearest base

Digital European Cordless Telephone



DECT features

• Developed by ETSI, a universal standard, finalized in 1992

• Cordless communications for High traffic density, allowing for high subscriber

densities

• Short range

• Low power access between portable and fixed parts

• Range up to a few hundred meters

• Broad range of applications and environment

– Good quality for both voice and data application

– speech quality comparable to wireline telephony,

• Provides local mobility to portable users in an in-building PBX

• Supports telepoint services

• DECT is configured around OSI, allowing it to interconnect wide area fixed or mobile

networks such as ISDN or GSM to a portable subscriber population

• a high level of security through advanced digital technology and encryption,

• Flexible bandwidth allocation,

• multiple service support, cost competitiveness, flexible deployment and simple

installation.

• The range of DECT applications includes residential, PSTN and ISDN access,

wireless PABX, GSM access, Wireless Local Loop, Cordless Terminal Mobility CTM,

Local Area Network access supporting voice telephony, fax, modem, E-mail,

Internet,X.25 and many other services in a cost efficient manner.

215

Digital European Cordless Telephone (Cont‘d)



• After the first edition of the DECT standard was available in 1992,

the DECT standardisation work concentrated on the definition of the

Generic Access Profile (GAP) and other interworking profiles

– DECT/GSM,

– DECT/ISDN,

– DECT/Radio Local Loop,

– CTM and several data profiles).

• This work and additional demands from the DECT market initiated

several extensions and enhancements

• to the base standard enabling even more effective application of

DECT products which led to the 2nd edition of the base standard

being finalised by the end of 1995.









216

Digital European Cordless Telephone (Cont‘d)



• To stimulate interoperability between DECT equipment

from different manufacturers ETSI members started to

work on the definition of standard interworking profiles by

the end of 1993.

• The Generic Access Profile GAP [9] was the first profile,

completed in 1994. It contains the protocol subset

required for the basic telephony service in residential

• cordless telephones, business wireless PABX, and

public access applications;

• It provides the basis for all other DECT speech

• profiles. Interoperability testing for GAP has

• been finished successfully.

217

Digital European Cordless Telephone

DECT Architecture



• Based on OSI, A control plane (C-plane) and user plane

(U-plane) use the services of lower layers:

– MAC layer

– Physical layer

• Paging capacity of up to 6000 subscribers

– Subscriber can be in any cell

– No need for registration

• Provides wireless local loop, or metropolitan area access

– May be used in conjunction with GSM

• Dynamic channel allocation, based on signals from

portables

• Designed to support hand offs only from pedestrians



218

Digital European Cordless Telephone

DECT Architecture: Physical layer

• Uses a FDMA, Time Division Multiple Access, Time Division Duplex

(FDMA/TDMA/TDD) radio access methodology.

• Basic DECT frequency allocation uses 10 carrier frequencies (FDM) in the

1880 to 1900 MHz range.

• DECT is subdivided into timeframes repeating every 10 ms. Each frame

consists of 24 timeslots each individually accessible (TDMA) that may be

used for either transmission or reception.

• For the basic DECT speech service, two timeslots - with 5 ms separation -

are paired to provide bearer capacity for typically 32 kbit/s (ADPCM G.726

coded speech) full duplex connections.

• To simplify implementations for basic DECT the 10 ms timeframe has been

split in two halves (TDD); where the first 12 timeslots are used for FP

transmissions (downlink) and the other 12 are used for reverse link

transmissions (uplink).

• Channel data rate = 1152 Kbps

• Channel bandwidth = 1152*1.5 = 1.728 MHz

• Each time slot has 480 bits = 1152*10/24

– 32 synch bits

– 388 data bits

– 60 bits guard time

219

•

TDMA Frame Structure









32 kbps*10 ms = 320 Bits

220

Digital European Cordless Telephone

DECT Architecture: MAC /DLC/Network layer

• MAC layer consists of

– A Paging and A control channel for the transfer of signaling info to the C-plane

– U-plane: served with channels for transfer of user information (Example: ISDN,

FR etc)

– The information rate is 32 Kbps. Higher rates (n*32 kbps) can be supported by

combining time slots

– Supports handover of calls, and broadcast beacon service that enables all idle

portable units to find the best fixed port to lock on to.

• Data link Control (DLC) control

– Provides reliable data links to the network layer,

– divides logical and physical channels into time slots for each user

– Provides formatting and error protection for each time slot

• Network Layer

– Main signaling layer

– Based on ISDN and GSM protocols

– Provides call control and circuit switched services selected from one of the DLC

services

– Connection oriented message services and mobility management

221

DECT Functional Concept

• Microcellular /picocellular cordelss subsystem that may integrate with PABX or to the

PSTN

• DECT always consists of:

– Portable Handset: Mobile terminal. Cordless terminal adapters (CTA) may be

used to provide FAX or video services

– Radio Fixed Part: Equivalent to a base station. Supports physical layer of the

DECT Common Air Interface. One per cell. The radio transmission uses multi

carrier TDMA. FDX by using TDD

– Cordless Controller (or cluster controller). Handles MAC, DLC and network layer

for one or cluster of RFPs

• Is a central control unit for the DECT equipment . Speech coding is done on

CC using 32 Kbps ADPCM

– Network Specific Interface unit: Supports the call completion facility in a multi

handset environment. Interface supported is G.732 based on ISDN standards

– Supplementary services:

• centralized AUTHENTICATION and Billing, if DECT used for Telepoint

services

• Mobility management when used in multilocation PBXs







Note: system is limited by C/I, the capacity may be increased

And interference may be reduced by installiting RFPs in Closer proximity 222

DECT Functional Concept









223

DECT Radio Link



• operating in the preferred 1880 to 1900 MHz band

• Ten channels from 1881.792 to 1897.344 Mhz are specified with a

spacing of 1728 Khz.

• Supports MC/TDMA/TDD

• Ecah base station provides a TDM frame which supports 12 duplex

speech channels

• Each time slot may occupy any of the DECT channels

• The base station supports FHMA on top of TDMA/TDD

• Without freq hopping, each DECT Base station supports 120

channels ( 10 freq, each supporting 12 duplex speech channels)

• Each time slot may be assigned to a different channel to take

advantage of freq hopping, and to avoid interference from other

users





224

DECT Radio Link (Cont‘d)

• Channel types: 320 bits of user data is transmitted in B-field time slots

• This supports 32 Kbps data stream per user

• Only 4 parity bits are used for user data protection

• DECT control info is carried in each time slot of an established call

– These bits are assigned to one of the 4 logical channels, depending on control

information type

– Control channel rate is 64 bits per 10 msecs = 6.4 Kbps.

• 1.6 kbps out of 6.4 kbps is used for CRC, and ).8 Kbps is for header information of the

control info.

• Speech Coding:

– 32 Kbps ADPCM is used (CCITT G.721 recommendation)

– For speech signals, no channel coding is used, as DECT provides freq hopping

for each time slot

• Channel coding and inter-leaving

– not used, as DECT is meant for indoor use, and delays are very small

– For control channels 16 bit CRC is sued









225

DECT Radio Link (Cont‘d)

Modulation

• DECT uses tightly filtered GMSK

– MSK is a form of FSK, where phase transitions between 2 symbols is

constrained to be continuous

– Guassian shaping filter is used ( BT =0.3)

• Antenna Diversity ( Not used for subscriber unit)

– Spatial diversity implemented at Base station using 2 antennas.

– Selective diversity ( antenna providing best signal for each time slot

– selected)

– Base station selection based on measures of signal strength of the

received signal to determine the best antenna ( Could be based on

interference also)









226

227

DECT Fixed Part Beacon function

Channel

utilization

Paging

Synchronization

System Identity



RFP

Radio Sys capabilities

Fixed Part









228

Digital European Cordless Telephone (Cont‘d)



Call set-up

Portable user originated call set-up

• The initiative to set-up radio links in basic DECT applications is

always taken by the portable part.

• The portable selects (using its Dynamic Channel Selection) the best

channel available for set-up, and accesses the fixed part on this

channel.

• To be able to detect the PP‘s set-up attempts the fixed part must be

receiving on the channel when the PP transmits its access request.

• To allow portables to use all 10 DECT RF carriers, the fixed part

continuously scans its idle receive channels for portable set-up

attempts in a sequential way.

• Portables synchronise to this sequence by means of the information

transmitted through the FP continuous broadcast service.

• From this information portables can determine the exact moment

when successful access the FP is possible on the selected channel.



229

Digital European Cordless Telephone (Cont‘d)

Call set up



Network originated call set-up

• When a call comes in for a DECT portable,the

access network will page the portable by

sending a page message –

• containing the PP‘s identity - through its

continuous broadcast service.

• A portable receiving a paging message with its

identity included will set-up a radio link - to serve

the incoming call –

– Using the same procedure as used for the PP

originated link set-up.



230

PWT



• The North American Personal Wireless

Telecommunications standards PWT and PWT/E (TIA)

are based on DECT. PWT and PWT/E provide the same

services as DECT

• They use the same framing structure MAC,

• DLC, NWK layer and identities

• but an alternative modulation scheme and frequency

• allocation.

• The PWT operates in the US unlicensed band 1910 to

1920 MHz.

• PWT/E is an extension into the licensed bands 1850 –

1910 MHz and 1930 - 1990 MHz.

231

References



http://www.dectweb.com/dectforum/publicdocs/TechnicalDocument.PDF#search='DECT%20standard‗





http://www.comsoc.org/pci/private/2000/jun/Hashemi.html









232

ETS 3000 175 Summary

Part Title Description

1 Overview General introduction to the other parts of ETS 300 175



2 Physical layer Radio requirements of DECT, e.g. carrier Fequency allocation,

modulation method, transmission frame structure, transmitted power

limits, spurious emission requirements etc.



3 MAC Description of procedures, messages, and protocols for radio resource

management i.e. link set-up, channel selection, handover, link release

and link quality maintenance etc.

4 Data Link Description of provisions to secure a reliable data link to the network

control Layer layer

5 Network Layer Description of the signalling layer with call control and mobility

management functions and protocols.

6 Identities and Description of the portable and fixed part identities requirements for all

addressing DECT application environments.

7 Security Procedures to prevent eavesdropping, unauthorised access and

Aspects fraudulent use.

8 telephony Telephony requirements for systems supporting the 3.1 kHz speech

service to ensure proper interworking with public telecommunications

networks. Defines transmission levels, loudness ratings, sidetone levels,

frequency response,

echo control requirements etc 233

Personal Access Communication System

PACS









234

Personal Access Communication System

PACS

• Originally developed by Bellcore in 1992

• PACS was developed in the United States and standardized

by the Joint Technical Committee (JTC) in 1994.

• Designed to integrate all forms of wireless Local loop (WLL),

communication into one system with full telephone features.

• Supports Voice, data and video images for indoor use and

microcell use

• Bellcore developed PACS concept with LECs in mind and

called it Wireless Access communication system

• Designed for a range of 500 meters

• It operates in two wide duplex bands, 1850–1910 MHz (uplink)

and 1930–1990 MHz (downlink).

• These bands were allocated by the FCC in three paired 5 MHz

and three paired 15 MHz bands for licensed wideband PCS

applications.

• Also, a 10 MHz band (1920–1930 MHz) has been allocated for

unlicensed TDD operation. The air interface of PACS allows

frequency-division duplex (FDD) operation in the licensed band

and TDD operation in the unlicensed band 235

Personal Access Communication System

PACS

• The PACS standard is based on FDD-TDMA with 200 channels (carrier

separation of 300 kHz).

• Modulation and speech coding are p/4-quadrature phase shift keying

(QPSK) and 32 kb/s ADPCM, respectively.

• Bit rate per channel is 384 kb/s. Channel assignment is quasi static

autonomous frequency assignment/dynamic channel assignment

(QSAFA/DCA)

• The standard is designed for low-mobility applications. However, operation

at high speed (several tens of kilometers per hour) is also possible.

Maximum transmission power of the portable unit is 200 mW, average

power 25mW.









236

PACS Architecture

• Universal wireless access system for public and private telephone systems

– Can connect to central office or PBX

• Allocated frequencies include licensed and unlicenses spectrum

• PACS architecture includes following components

– Subscriber unit (fixed or portable)

– Radio port

– Radio port control unit (Radio port Connected to RPCU)

– Access manager

• Interface A provides radio interface between subscriber unit and radio port

• Interface P supports protocols required to connect SU to RPCU through RP

– Also connects RP to RPCU by using an embedded operation channel provided

within the interface

• PACS standard contains a fixed distribution network and network

intelligence.

• Only the last 500metrs of the distribution network is wireless









237

PACS System Architecture









238