A MULTICARRIER CDMA ARCHITECTURE BASED ON
ORTHOGONAL COMPLEMENTARY CODES FOR NEW GENERATION
OF WIDEBAND WIRELESS COMMUNICATIONS
• BY: COLLINS ACHEAMPONG
• GRADUATE STUDENT
• TO: Dr. Lijun Quin
• DEPT OF ELECTRICAL ENGINEERING
• PRAIRIE VIEW A&M UNIVERSITY
• PRAIRIE VIEW, TEXAS
• A RESEARH PROJECT
• WIRELESS NETWORKS
• FALL 2003 SEMESTER
• PROBLEM STATEMENT
• METHOD OF SOLVING PROBLEM
• BASIC CODE DIVISION MULTIPLE ACCESS (CDMA) SYSTEM
• SPREAD SPECTRUM FUNDAMENTALS
• COMPLETE COMPLEMENTARY CODES
• MULTIPATH SELF-INTERFERENCE
• ANALYSIS OF MODEL PARAMETERS AND RESULTS
• LIMITATIONS, ADVANTAGES, AND REMARKS
• The proposed Multicarrier Code Division multiple access (MC-CDMA) has a great
potential for applications in future wideband mobile communications beyond Third
Generation (3G), which is expected to offer a very high data rate in hostile environment.
• The paper is a continuation of on going research effort to construct a Multicarrier
CDMA architecture based on orthogonal complementary codes, characterized by its
unique spreading modulation scheme, uplink and downlink signature design, and
receiver implementation for multipath signal detection.
The ongoing research was first conducted by:
Hsiao-Hwa, National Sun Yat-Sun University
Jun-Feng, National Chung Hsing University
Naoki Suehiro, Yeh, National University of Tsukuba
• Code Digital Multiple Access (CDMA) is a predominant multiple access
technique proposed for the 3G wireless communication systems worldwide.
• The maturing of 3G mobile communication technologies from concepts to
commercially deliverable systems motivates us to think about the possible
architectures for future generations of mobile wireless.
• The question is how to guarantee such high data rate in highly unpredictable
and hostile channels?
• What types of air link architecture are qualified to deliver such high-data-rate
• The new MC-CDMA architecture that has a great potential for future mobile
communications tackles this issues comprehensively.
• The new CDMA architecture ought to be technically feasible with current
available digital technology.
• The proposed CDMA system should preferably have an inherent ability to
mitigate path problems in mobile channels.
• It can achieve spreading efficiency (SE) very close to one
• It offers Multiple Access Interference (MAI) free operation in both up
and down link transmission in a MAI-AWGN (Additive White
• Able to offer high bandwidth efficiency due to its use of unique
spreading modulation scheme.
• It is particularly suited to multi-rate signal transmission due to the use
of an offset stacked modulation scheme.
Mothod of Solving Problem
• Use of direct sequence orthogonal complete complementary codes.
• The bit error rate (BER) of the proposed CDMA system under MAI and
Additive White Gaussian Noise (MAI-AWGN) is evaluated using computer
• The obtained BER performance of the new CDMA system will be compared
to the conventional CDMA system using Gold codes and m-sequences under
identical operation environments
BASIC CODE DIVISION MULTIPIPLE ACCESS (CDMA)
• CDMA IS A SPREAD SPECTRUM COMMUNICATIONS TECHNIQUE
THAT SUPPORTS SIMULTANEOUS DIGITAL TRANSMISSION
• CDMA IS SIMILAR TO THAT OF FDMA (FREQUENCY DIV.
MULTIPLE ACCESS) AND TDMA (TIME DIV. MULTIPLE ACCESS).
• CDMA HAS THE UNIQUE PROPERTY OF SUPPORTING A
MULTIPLICITY OF USERS IN THE SAME RADIO CHANNEL
• CDMA HAS GRACEFUL DEGRADATION IN PERFORMANCE DUE TO
• FREQUENCY RE-USE FACTOR IN CDMA CELLULAR ENVIRONMENT
CAN BE AS HIGH AS UNITY.
• CDMA BEING A WIDEBAND SYSTEM CAN CO-EXIST WITH OTHER
NARROWBAND MICROWAVE SYSTEMS
• THE MOST ADVANTAGE OF CDMA IS ITS ABILITY TO COMBAT
FROM MULIPATH FADING.
• CDMA system allows unique pseudo-noise codes to individual users
• Any user is allowed to access the air at ant time
• Spreading efficiency (SE) for all conventional CDMA equals 1/N
which is less than one.
• Low rate data symbols are multiplexed by CDMA code resulting in a
wideband waveform – “a process known as spreading”
• Multi-code methods assigns one or more codes with fixed spreading
factor to any one user.
• This results in a waveform with high peak power.
• A users requiring high throughput is allocated a CDMA code with a
low spreading factor
• CDMA codes may be time slotted to regulate access.
Figure 1. CDMA in the code and time domain
S0 S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11S12 S13 S14 S15 S16
Figure 1: CDMA in the code and time domain
Spread Spectrum Fundamentals
• Originally develop for military applications to provide anti-jam.
• Qualcom Inc., developed it in the late 1980’s and early 1990’s which led to
IS-95 cellular standard.
• Spread spectrum characteristic:
• Bandwidth used is much greater than the message bandwidth.
• Bandwidth spreading is achieve by using a spreading code or (pseudo-
noise) p-n sequence, while the spreading code is independent to the
• Two types of spread spectrum are:
• Direct sequence (DS) and Frequency hopped (FH) spread spectrum.
• DS uses p-n sequence to introduce rapid phase transition into the carrier
containing the data.
• FH uses p-n sequence to pseudo randomly hop the carrier frequency
throughput a large band.
• The original information signal which occupies a bandwidth of B Hz is transmitted
after spectral spreading to the bandwidth N times higher.
• N is known as the processing gain typically in the range of 10-30 dB.
• Power of transmitted spread spectrum is spread over N times the original
bandwidth while its density is correspondingly reduced by the same amount.
• Hence, the processing gain is given by N = Bs/B, where Bs is the bandwidth of
spectral signal while B is the original information signal.
• The unique technique of spreading is the key to improving its detection in a mobile
• This allows narrowband signals exhibiting higher spectral density to share the same
• Hence, the spectral efficiency is defined as:
bits / s / Hs
where Rd is the transmitted data rate, and Brf the system bandwidth.
COMPLETE COMPLEMENTARY CODES
• Use of direct sequence orthogonal complete complementary codes
• The orthogonal complete complementary code is based on a “flock” of
element codes jointly instead of a single code as in traditional CDMA.
• Each user in the MC-CDMA system will be assigned a flock of element
codes as its signature code.
• Each bit is spread by one single continuous code comprising of N
contiguous chips to attain certain processing gain or spreading factor.
• User that require higher throughput is allocated more codes with lower
• Codes ought to be transmitted possibly via different frequency channels,
and arrive at a receiver at the same time.
• The information bits correlator are spreading modulated by element
codes that are “offset stacked”, each shifted by one chip relative to one
• Every signature code is spread into several segments (or element code)
• New bits will start right after one chip is delayed relative to the previous
• Bit is spread by element code length L.
• The bit error rate (BER) under the MAI and AWGN is evaluated using
COMPLETE COMPLEMENTARY CODES
Element code length L, = 4 Element code length L = 16
Processing gain are equal to 4x2 = 8 and 16x4 = 64 respectively
Flock 1 A0: + + + - Flock 1 A0: + + + + + - + - + + - - + - - +
A1: + - + - + + + + + - - + + + - -
A2: + + - - + - - + + + + + + - + -
A3: + - - + + + - - + - + - + + + +
A1: + - + + Flock 2 B0: + + + + - + - + + + - - - + + -
B1: + - + - - - - - + - - + - - + +
B2: + -+ - - - + + - + + + + - + - +
B3: + - - + - - + + + - + - - - -
Flock 2 B0: + + - + Flock 3 C0 : + + + + + - + - - - + + - + + -
C1: + - + - + + + + - + + - - - + +
C2: + + - - + - - + - - - - - + - +
C3: + - - + + + - - - + - + - - - -
B1: + - - - Flock 4 D0: + + + + - + - - + + + - - +
D1: + - + - - - - - - + + - + + - -
D2: + + - - - + + - - - - - + - + -
D3: + - - + - - + + - + - + + + +
Table 1. Two examples of complete complementary codes
with element code lengths L = 4 and L = 16
Performance Analysis Under Multiple Access Interference
• Compared with traditional spreading modulation used in conventional
CDMA systems, the new system has the following salient features:
• The new system is no longer aligned in time one bit after another.
• Instead a new bit will start right after one chip delay relative to the
previous element L.
• The unique offset stacked spreading method can easily slow down data
transmission by simply shifting more than one chip (at most L chips)
between two neighboring offset stacked bits.
• Thus, the MC-CDMA architecture is capable of delivering much higher
bandwidth efficiency than a conventional CDMA architecture under the
same processing gain.
• The “inherent” ability of the MC-CDMA system to facilitate multirate
transmissions is based on its innovative offset stacked spreading
technique, which cannot be applied to traditional spreading codes.
• The MAI-independent property is significant in terms of its potential to
enhance its system capacity in a multipath channel in MC-CDMA.
• CDMA rake receiver achieves perfect diversity gain from multipath
reception if it can perfectly decouple the different paths.
• In practice however, each path acts as interference for other paths.
• Interference becomes especially significant if the CDMA signal is
transmitted over many code channels or the spreading factor is small.
• Conventional CDMA receiver usually uses a Rake receiver to collect
dispersed energy among different reflection paths to achieve multipath
diversity at the receiver.
• Therefore, the Rake receiver is a must for all conventional CDMA
systems, including current operational 2G and 3G systems.
• In MC-CDMA architecture, the Rake receiver becomes inappropriate
due to the nature of the unique spreading modulation technique
employed in the system.
• CDMA technology requires the use of power control for subscriber terminals.
• The effectiveness of power control determines the capacity of the network.
• In CDMA if one terminal transmit excessive power, it increases the
interference on all other remaining terminals and reduces their link quality.
• In ODFM power control is not as critical as CDMA.
• There is no fundamental requirement for the use of power control since the
user terminals in the same sector do not share the same frequency at the same
• Reason for using power control in an OFDM system is to minimize co-channel
A Multicarrier CDMA Architecture
Figure 10: MC-CDMA simulation used for forward traffic
ANALYSIS OF MODEL PARAMETERS AND
Figure 13: The simulation in operation
This is the start of the simulation for MC-CDMA (with BER values shown) in Figure 13.
Comparison of MC-CDMA and CDMA Spread Model
CDMA and MC-CDMA Comparison Summary
Spectral efficiency More efficient Less efficient
Multipath Handles larger number of paths Some diversity benefits; performance
sensitivity to number of path coherently
Multiple Modulation support Downlink and Uplink Downlink only
Resistance to Narrowband Suited for multirate signal Spread spectrum provides that
Interference transmission due to the use of an offset
stacked spreading modulation scheme
Network Planning It simplifies the rate-matching Difficult for cell overlays; PN offset
algorithm relevant to multimedia planning cell-breathing complications
services and asymmetric traffic in up
and downlink transmission for IP-
Power Control Required function Required function
Peak-to-Average Ratio Varies Varies; can be as high as 11dB
Standards Adoption WLAN, 3G, 4G WLAN, 3G
Cost Less expensive Varies, may depend modem.
The Bit Error Rate (BER) Test Results for MC-CDMA
TX Error 1 2 3 4 5 6 7
BER 0 0.00072 0.00833 0.00227 0.00077 0.00091 0.00119
Error Count 0 0 1 2 3 4 6
Sample Count 0 80 120 880 3880 4360 5040
Total Sample T=0.085
The Bit Error Rate (BER) Test Results for CMDA
Number of 1 2 3 4 5 6
BER 0 0 0.0174 0.0290 0.03516 0.0195 0.01896
Error Count 0 0 30 85 127 131 137
Sample 0 1032 1720 2924 3612 6078 7224
Sample time secs
There exit some technical limitations for the proposed cc-codes based MC-
CDMA which ought to be addressed.
If a long cc-code is employed in the MC-CDMA system, the number of
different levels generated from the baseband could be a problem.
For example, cc-codes with L = 4 will generate five possible levels from the
“offset stacked” spreading; 0, ±2 ,and ±4.
For cc-code with L=16 becomes 0, ±2, ±4 ±16, comprising 17 different levels.
In general, it will yield L+1 different levels.
Another concern is with the cc-code based CDMA is that, a relatively small
number can be supported by a family of cc-codes.
For cc-codes family with L = 64, only eight flock of codes, each of which can
be assigned to one channel. If more users should be supported, long cc-codes
have to be used.
The cost for introducing a multilevel digital modem may be expensive varies
depending on a user’s requirements.
Advantages and Remarks
The MC-CDMA can achieve spreading efficiency very close to one.
It offers multiple access interference (MAI free operation in both up and down link
transmission in MAI-AWGN channel.
It can significantly reduce reduce the co-channel interference responsible for capacity
decline in CDMA systems.
Able to offer high bandwidth efficiency due to its use of unique spreading modulation
Particularly suited for multi-rate signal transmission due to the use of an offset stacked
One possible solution to the MC-CDMA problem is to introduce a of multilevel digital
modem capable of transmitting L+1 different levels in a symbol duration. An L+1
quadrature modulation (QAM) digital modem can be a suitable choice for its robustness
in detection efficiency.
Another possible solution is to introduce frequency division on top of the code division
in each frequency band to create more transmission channels.
• The paper addresses several advantages of the MC-CDMA over conventional
CDMA such as higher bandwidth efficiency, MAI-free operation in both
synchronous and asynchronous MAI_AWGN channels.
• Also reduces co-channel interference and capacity increase in mobile cellular
• The paper addresses technical limitations of the new MC-CDMA architecture,
such as relatively small family codes and the need for complex multilevel
• Both CDMA and the MC-CDMA both have their respective advantages.
• Nevertheless, the proposed MC-CDMA architecture based on complete
complimentary codes offers a new option to implement future wideband
mobile communications beyond 3G.
• Future research work on this paper will be needed to be continued as I could
not find all the answers to limitation problems.
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Architecture Based on Orthogonal Complementary Codes for New Generation
Wideband Wireless Communications,” IEEE Communication Magazine,
October 2001, Page 126-134.
• 2. P. Nicopolidis, M.S. Obaidat, and A. S. Pomportsis, “Wireless Networks,”
Institute of Electrical Engineers, Inc, New York, NY 2001; Pages 365-389.
• 3. Young-Hwan You, Won-Gi Jeon, Jung-Work Wee, and Hyeok-Koo Jung,
“Effect of Diversity Technique on Performance of OFDM-CDMA Base
Broadband Wireless Access Networks,” IEICE Transaction Communication,
Vol. E86-B. No.4, April 2003, Pages 1402-1404.
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Communications: second to third generation systems and beyond,” IEEE, Inc.
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Access in IEEE 802.16,” IEEE Communication Magazine, April 2002, pages