PES INSTITUTE OF TECHNOLOGY, BANGALORE-560085
Subject: Wireless and Mobile Networks Code: 10EC0131
Class: II SEM MTECH Staff: Kavitha Y.C
INTERNAL TEST- 3 SOLUTIONS
1. a). What are the advantages of IEEE802.16 (5 Marks)
i. Last-mile connectivity
For many home and business customers, broadband access via DSL or cable infrastructure is still not available.
Many customers are outside the range of DSL's reach and/or are not served by broadband-capable cable infrastructure.
Practical limitations prevent cable and DSL technologies from reaching many potential broadband customers. Traditional
DSL can only reach about 18,000 ft (3 miles} from the central office switch, and this limitation means that many urban and
suburban locations may not be served by DSL connections. However, with wireless broadband these problems can be
solved. Due to its wireless nature, it can be faster to deploy, easier to scale, and more flexible, thereby giving it the potential
to serve customers who were not served or not satisfied by their wired broadband alternatives. 802.16 standards help to
solve the last-mile problems. Last-mile broadband wireless access can help to accelerate the deployment of 802.11 hotspots
and home/small office WLANs.
ii. Roaming between networks
802.16e enables "handoff" procedure that allows a mobile device to switch the connection from one BS to
another, from one 802 network type to another (such as from 802.lib to 802.16), and even from wired to 802.11 or
802.16 connections. Today, 802.11 users can move around a building or a hotspot and stay connected, but if they leave,
they lose their connection. With 802.16e, users will be able to stay "best connected" by 802.11 when they are within a
hotspot, and then connected to 802.16 when they leave the hotspot but are within a WiMAX service area. 802.16e
capabilities embedded in a persona! digital assistant (PDA) or notebook (or added through an 802.16e-enabled card) will
enable a user to remain connected within an entire metropolitan area. For example, a notebook could connect via Ethernet
or 802.11 when docked, and stay connected with 802.16 when roaming the city or suburbs.
802.16 standard will also provide an important flexibility advantage to businesses that move their operations
frequently, like a construction company with offices at each building site. Instead of waiting weeks for DSL line, wireless
broadband access can be quickly and easily set up at new and temporary sites.
The 802.16 standard is scalable. To accommodate easy cell planning in both licensed and license -exempt
spectrum worldwide, 802.16 supports flexible channel bandwidths. For example, if an operator is assigned 20 MHz of
spectrum, the operator could divide it into two sectors of 10 MHz each or four sectors of 5 MHz each. By focusing power
on increasingly narrow sectors, the operator can increase the number of users while maintaining good range and
1.b). Differentiate between IEEE 802.16 and IEEE 802.11 (5 Marks)
1 WiMAX uses licensed or unlicensed spectrum to deliver a point-to-point (P2P) connection to the Internet from an Internet
service provider (1SP) to an end-user. Different 802.16 standards provide different types of access, from portable to fixed
terminal. WiMAX is developed primarily for WMAN, with a transmission range in order of a few kilometers. Wi-Fi uses
unlicensed spectrum to provide access to a network. Wi-Fi has primarily been developed for WLAN, with the transmission range
of upto 100 m. Wi-Fi therefore is often used for last-mile delivery, such as in hotspot.
2. WiMAX and Wi-Fi have quite different QoS mechanisms. WiMAX uses a mechanism based on connections between the BS and
the user device. Each connection is based on specific scheduling algorithms. Wi-Fi has introduced a QoS mechanism similar to
fixed Ethernet, where packets can receive different priorities based on their tags. For example, VolP traffic may be given priority
over web browsing.
3. Wi-Fi runs on the MAC's carrier sense multiple access with collision avoidance (CSMA/CA) protocol, which is connectionless
and contention-based, whereas WiMAX runs on a connection-oriented MAC.
2). Explain the features of WIMAX (10 Marks)
1. Flexible architecture:
WiMAX supports several system architectures, including P2P, P2MP, and ubiquitous coverage. The WiMAX MAC (to be
discussed later) supports P2MP and ubiquitous service by scheduling a time slot for each SS. If there is only one SS in
the network, the WiMAX BS will communicate with the SS on a P2P basis. A BS in a P2P confi guration may use a
narrower beam antenna to cover longer distances.
2. High security:
WiMAX supports Advanced Encryption Standard (AES) and Triple Data Encryption Standard (3DES). By encrypting the
links between the BS and the SS, WiMAX provides subscribers with privacy (against eavesdropping) and security across
the broadband wireless interface. Security also provides operators with strong protection against theft of service.
WiMAX also provides protection for data that are being transmitted by different users on the same BS.
3. WiMAX QoS:
WiMAX can be dynamically optimized for the mix of traffic that is being carried. Five types of services are supported;
unsolicited grant service (UGS), real-time polling service (rtPS), extended real-time polling service (ertPS), non-real-time
polling service (nrtPS), best effort (BE) service.
4. Quick deployment:
Compared with the deployment of wired solutions, WiMAX requires little or no external plant construction. For
example, excavation to support the trenching of cables is not required. Operators that have obtained licenses to use one
of the licensed bands, or plan to use one of the unlicensed bands, do not need to submit further applications to the
government. Once the antenna and equipment are installed and powered, WiMAX is ready for service. In most cases,
deployment of WiMAX can be completed in a matter of hours compared with months for other solutions.
5. Multilevel service:
The manner in which QoS is delivered is generally based on the service level agreement (SLA) between the service
provider and the end-user. Furthermore, one service provider can offer different SLAs to different subscribers or even to
different users on the same SS.
WiMAX is based on international, vendor-neutral standards that make it easier for end-users to transport and use
their SS at different locations, or with different service providers. Interoperability-protects the early investment of an
operator as it can select equipment from different equipment vendors, and it will continue to drive the costs of
equipment down as a result of mass adoption.
As with current cellular systems, once the WiMAX SS is powered up, it identifies itself, determines the characteristics of
the link with the BS, as long as the SS is registered in the system database, and then negotiates its transmission
The IEEE 802.16e amendment has added key features in support of mobility. Improvements have been made to the OFDM
and orthogonal frequency division multiple access (OFDMA) PHY layers (to be discussed later) to support devices and services
in a mobile environment. These improvements, which include scalable OFDMA, MIMO, and support for idle/sleep mode
and handoff, will allow full mobility at speeds up to 160 km/h. The WiMAX Forum-supported standard has inherited
OFDM's superior NLOS performance and multipath-resistant operation, making it highly suitable for the mobile
WiMAX is based on an open, international standard. Mass adoption of the standard, and the use of low-cost mass-
produced chipsets, will bring costs down dramatically, and the resultant competitive pricing will provide considerable cost
savings for service providers and end-users.
10. Wider coverage:
WiMAX dynamically supports multiple modulation levels, including binary phase-shift keying (BPSK), quadrature phase-shift
keying (QPSK), 16 QAM, and 64 QAM. When equipped with a high-power amplifier and operating with a low-level
modulation (BPSK or QPSK, for example), WiMAX systems are able to cover a large geographic area when the path between
the BS and the SS is unobstructed.
11. NLOS operation:
WiMAX is based on QFDM technology, which has the inherent capability of handling NLOS environments. This capability
helps WiMAX products deliver broad bandwidth in an NLOS environment, which other wireless products cannot do.
12. High capacity:
Using higher modulation (64 QAM} and channel bandwidth, WiMAX systems can provide significant bandwidth to end-
3). What are the IEEE 802.16 physical layer interface variants? (10 Marks)
This is the only PHY layer specification defined to operate in 10-66 GHz frequency band .
It employs single-carrier modulation with adaptive burst profiling, in which transmission parameters,
including the modulation and coding schemes, may be tuned individually to each SS on a frarne-by-
The standard supports both FDD and TDD to separate UL and DL.
The standard also supports half-duplex FDD, which may be less expensive as it does not transmit and
This is also based on single-carrier modulation targeted for 2-11 GHz frequency range.
Access is done by TDMA technique both in UL and DL; TDM is also supported in DL.
This is based on OFDM with a 256-point transform to support multiple SSs in 2-11 GHz frequency band.
Access is done by TDMA.
The WiMAX forum has adopted this PHY layer specification for broadband wireless access.
Due to employing OFDM and other features like multiple FEC method, this is the most suitable
candidate to provide fixed support in NLOS environment.
WM AN-OFDM A:
This PHY layer specification uses OFDMA with at least a single support of specified multipoint transform
(2048, 1024, 512, or 128J to provide combined fixed and mobile broadband wireless access.
Operation is limited to below 11 GHz licensed band.
This wireless high-speed unlicensed metropolitan access network (WHUMAN) specification is targeted
for license-exempt band below 11 GHz.
Any of the air interfaces specified for 2-11 GHz can be used for this.
This supports only TDD for duplexing
4). What are the advantages and disadvantages of LMDS and MMDS (10 Marks)
Advantages of MMDS spectrum are as follows:
1. Propagation over long distances up to 100 km with single owner.
2. Less attenuation due to rain, foliage.
3. RF component costs lower at 2.5 GHz, and equipment readily available today.
Disadvantages of MMDS spectrum are as follows:
1. Limited capacity without sectorization, and Cellularization which adds complexity and cost.
2. Interference issues with other MMDS and instructional television fixed service (ITFS)
3. Large upstream bandwidth in MMDS band requires careful planning, filtering, etc.
4. Cellularization later on may require retuning the entire network
Advantages of LMDS spectrum are as follows:
1. Very large bandwidth available for data, IP telephony, and video conferencing services.
2. Large capacity.
Disadvantages of LMDS spectrum are as follows:
1. Higher RF component costs.
2. Small cell size, 2-8 km.
3. Does not cover entire metropolitan area of a target city without adding many cells at high
5). What are the silent features of satellite networks (10 Marks)
A satellite may cover global, regional, or national geographical areas.
All services include simplex or duplex, balanced or asymmetric links from 64 kbps-45 Mbps. Higher rate services are also
possible in selected coverage areas.
Carrying IP traffic over satellites poses the same degree of security risks as sending it over a terrestrial connection. If
security is a concern then you can use encryption, a process of electronically altering a signal from its original condition
to prevent unauthorized use. There is no encryption on the satellite links but there are a variety of companies that can
provide encryption software for the traffic. This is a common practice for banking and credit card and sales transactions
over the web.
4. Service types:
Service types offered by a satellite are fixed service satellite (FSS), broadcast service satellite (8SS), and mobile service
General usage of satellite networks are: commercial, military, amateur, experimental. Applications such as mobile
services, direct broadcast, private networks, and high-speed hybrid networks in which services would be carried via
integrated satellite-' fiber networks are being considered,
A communication satellite functions as an overhead wireless repeater station that provides a microwave communication
link between two geographically remote sites. Owing to its high altitude, satellite transmissions can cover a wide area
over the s of the Earth. Each satellite is equipped with various "transponders" consisting transceiver and an antenna tuned
to a certain part of the allocated spectrum incoming signal is amplified and then rebroadcasted on a different frequency,
satellites simply broadcast whatever they receive, and are referred to as "bent pi|
7. Packet switched:
The traditional applications were TV broadcasts and voice tele Satellite communications for packet data transmissions
are being considered, just packet networks.
8. Frequency band:
Satellites transmit information within radio frequency band: frequency bands most used by satellite communications
companies are called C-bar the higher Ku-band. Over the next several years, the use of a higher frequency known as Ka-
band is expected to increase. L/S band is used for terrestrial communication between satellite equipments. Modern satellites
are designed to focus on different of frequency bands and different power levels at particular geographic areas, The some
common frequency bands.
6) Differentiate between WLAN and WWAN (10 Marks)
Wireless local area networks (WLANs) operate over a small, "local" coverage area, normally about 100 m in range.
They are typically used in buildings to replace an existing wired Ethernet, or in a home to allow multiple users
access to the same Internet connection.
Other WLAN coverage areas can include public hotspots in coffee shops or some city neighborhoods.
WWANs cover a much "wider" area, such as wherever the cellular network provider has wireless coverage.
Typically, this is on a regional, nationwide, or even global scale. Using a WWAN usually gives the users access to
data wherever they go and is one of the biggest advantages of a wide area network
WWAN’s biggest strength is security
WLAN’s greatest weakness is security
WLAN(11Mbps) are faster than WWAN(115Kbps)
There is no service cost for using a private WLAN (such as in a corporate office or home office).
There will be a monthly Internet service provider cost for accessing the Internet through one's WLAN access point.
The other main cost involved is the cost of purchasing and installing the WLAN equipment and devices, and the cost
of maintaining the network and the users.
For cellular WWANs, the wireless network is acting as one's Internet service provider by providing access to the
Internet over one's wireless network.
The wireless provider therefore charges a monthly subscription rate to their network, similar to a wireless phone
This may be a flat monthly fee for the time when connected to the network or per megabyte of data transferred.
7) Mention key features of GPRS. (10 Marks)
1. . Speed:
Theoretical maximum speeds up to 171.2 kbps are achievable with GPRS using all eight time slots (of GSM) at the same time.
This is about three times as fast as the data transmission speeds possible over today's fixed telecommunications networks and
10 times as fast as current circuit-switched data services on GSM networks. By allowing information to be transmitted more
quickly, immediately, and efficiently across the mobile network, GPRS may well. be a relatively less costly mobile data
service compared to SMS and circuit-switched data.
GPRS facilitates instant connections whereby information can be sent or received immediately 3$ the need arises, subject to
radio coverage. No dial-up modem connection is necessary. This is why GPRS users are sometimes referred to be as being
"always connected," Immediacy is one of the advantages of GPRS (and SMS) when compared to circuit-switched data. High
immediacy is a very important feature for time critical applications such as remote credit card authorization where it would
be unacceptable to keep the customer waiting for even extra 30 s.
3. New and better applications:
GPRS facilitates several hew applications that have not previously been available over GSM networks due to the limitations
in speed of circuit-switched data (9.6 kbps) and message length of the SMS (160 characters). GPRS fully enables the Internet
applications for those who are used to their desktop from web browsing to chat over the mobile network. Other new
applications for GPRS include file transfer and home automation - the ability to remotely access and control in-house
appliances and machines.
4. Service access:
To use GPRS, users specifically need a mobile phone or terminal that supports GPRS, a subscription to a mobile telephone
network that supports GPRS. Use of GPRS must be enabled for that user. Automatic access to the GPRS ma by some mobile
network operators, others will require a specific option. It GPRS, the destination is not only a mobile phone but could also be
a com on some other network.
5. Packet switching:
GPRS involves overlaying a packet-based air interface or circuit-switched GSM network. This gives the user an option to use
a packet service. To supplement a circuit-switched network architecture with packet quite a major upgrade, GPRS standard is
delivered in a very elegant manner, operators needing only to add a couple of new infrastructure nodes are software upgrade
to some existing network-elements.
6. Spectrum efficiency:
Packet switching means that GPRS radio resources are used when users are actually sending or receiving data. Rather than
dedicating a radio channel to a mobile data user for a fixed period of time, the available radio resources concurrently shared
between several users. This efficient use of scarce radio resources means that large numbers of GPRS users can potentially share
the same bandwidth and be served from a single cell. The actual number of users' support depends on application being used
and how much data are being transferred.
7. Internet aware:
GPRS fully enables mobile internet functionality by allowing between the existing Internet and the new GPRS network.
Any service that the fixed Internet today - file transfer protocol (FTP), web browsing, chat, e mail will be available over the
mobile network because of GPRS.
8. Supports TDMA and GSM:
GPRS is not the only service designed to be the mobile networks that are based on the GSM digital mobile phone standard-
136 TDMA standard also supports GPRS. This follows an agreement to toiler evolution path toward 3G mobile phone
8). Give the features of CDPD (10 Marks)
1. Full duplex:
The communication from MS to BS and vice versa is operated in full duplex mode, that is, transmission can take both ways simultaneously
similar to GPRS and GSM
CDPD grabs 30 kHz channel temporarily from the existing voice networks such as GSM and digital AMPS for sending data .frames at a rate
of 19.2 kbps.. The net data rate is closer to 9.6 kbps.
In CDPD (data) mode, the mobile phone is data centric. The phone receive text messages or data, initiate a data session, or place an
outgoing voice There is no registration delay before data access as the phone is already register the CDPD network. To return to data
operation .after you have .placed a voice cal must press the END/BACK key to terminate the voice call. data without delay- At times in
dual mode operation, the phone may not be available for incoming voice calls for a brief period of time because it is maintaining and
updating its CDPD network registration.
Three kinds of interfaces are defined in CDPD: E-interface (external to CDPD provider) connects a CDPD area to a fixed network,-
I- interface (internal to CDPD) connects two CDPD areas together. A-interface (air interface) is between MS and BS. Data over the
air interface are sent using compression, encryption, and error-correction techniques.
5. Digital sense multiple access:
It is used to prevent all the MSs from jumping on the uplink channel (MS-BS) as soon it goes idle. When an MS has a frame to send,
It watches the downlink channel for a flag bit telling whether the current uplink slot is busy or idle. If it is busy, instead of just
waiting for next time slot, it skips a random number of slots and tries again.
6. Data users are preempted:
When a new voice call is about to be assigned to a channel currently in use for CDPD, the BS sends a special signal on the downlink,
closing down the channel. This is due to the fact that CDPD was added to operational voice systems.
It provides different kinds of packet-switched data transmission services and access to Internet.