A comparison of multiple access techniques in the presence of narrowband interference
29 Sep 1998-pp 223-228
TL;DR: The results indicate that contrary to a common belief, CDMA with pseudo-noise spreading sequences is more sensitive to narrowband interference than is TDMA, and the results confirm the superiority of OFDMA to all other multiple access techniques in this environment.
Abstract: This paper presents a comparison of several multiple access techniques in the presence of narrow-band interference. The analysis covers time-division multiple access (TDMA), code-division multiple access (CDMA), and orthogonal frequency-division multiple access (OFDMA). The results indicate that contrary to a common belief, CDMA with pseudo-noise spreading sequences is more sensitive to narrowband interference than is TDMA. Another finding is that orthogonal CDMA behaves similarly to OFDMA in the sense that the degradation is not the same for all users. Finally, the results confirm the superiority of OFDMA to all other multiple access techniques in this environment.
Citations
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TL;DR: This article describes some newly introduced concepts which allow us to accommodate N users without any interference while also accommodating additional users at the expense of some SNR penalty.
Abstract: Multiple access techniques which allow a communication medium to be shared between different users represent one of the most challenging topics in digital communications. In terms of the number of users that can be accommodated on a given channel, there are two distinct classes of multiple access techniques. The first class includes the well-known FDMA, TDMA, and OCDMA. On a channel whose bandwidth is N times the bandwidth of the individual user signals, these techniques can accommodate N users without any mutual interference, but not a single additional user can be supported beyond this limiting number. The second class includes CDMA with pseudo-noise spreading sequences (which we refer to as PN-CDMA) and some other related schemes. PN-CDMA does not have a hard limit on the number of users that can be accommodated, but is subject to multi-user interference which grows linearly with the number of users. In this article, after reviewing the capacity limits of existing multiple access techniques, we describe some newly introduced concepts which allow us to accommodate N users without any interference while also accommodating additional users at the expense of some SNR penalty.
112 citations
Additional excerpts
...Yet, using continuous-wave (CW) interference, it is clearly demonstrated in [ 11 ] that for a given interference power, the SIR at the threshold With channel...
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02 May 2004
TL;DR: An extended overview on the orthogonal frequency division multiple access (OFDMA) technique and its applications in 4/sup th/ generation cellular mobile networks is presented and a comparison between the performance of OFDMA and other multiple access systems is carried out.
Abstract: An extended overview on the orthogonal frequency division multiple access (OFDMA) technique and its applications in 4/sup th/ generation cellular mobile networks is presented. After introducing the main idea, a comparison between the performance of OFDMA and other multiple access systems is carried out. Moreover, some practical notes for system deployment are discussed. Finally, two standardized telecommunication systems that use OFDMA as air interface are introduced and their basic parameters are compared.
41 citations
08 Nov 1998
TL;DR: It was found that OCDMA can support a significant number of users at interference values which break both TDMA and PN-CDMA and the fact that OFDMA is the most resistant multiple access technique to narrowband interference.
Abstract: We investigate the influence of narrowband interference on different multiple access techniques including classic frequency-division multiple access (FDMA), time-division multiple access (TDMA), code-division multiple access (CDMA), and orthogonal FDMA (OFDMA). A major finding of this study is that CDMA with pseudonoise spreading sequences (PN-CDMA) does not perform any better than TDMA and that both multiple access schemes give virtually identical performance. We give a supporting interpretation of this result pointing out that TDMA is a special case of CDMA and that the argument of increased robustness to narrowband interference through spectral spreading equally applies to TDMA. Another finding is that orthogonal CDMA (OCDMA) has an entirely different behavior from TDMA and PN-CDMA in that the performance degradation is not the same for all users. Using continuous-wave (CW) interference, it was found that OCDMA can support a significant number of users at interference values which break both TDMA and PN-CDMA. We also point out some similarities between OCDMA and OFDMA, and highlight the fact that OFDMA is the most resistant multiple access technique to narrowband interference.
4 citations
01 Jan 2012
TL;DR: This chapter addresses the issues on the architecture of next generation CDMA (NG-CDMA) systems, which should offer a much better performance in terms of its capacity and transmission rate, etc., than that possible in all current 2-3G systems based on CDMA technology.
Abstract: This chapter addresses the issues on the architecture of next generation CDMA (NG-CDMA) systems, which should offer a much better performance in terms of its capacity and transmission rate, etc., than that possible in all current 2-3G systems based on CDMA technology. The ultimate goal is to engineer a CDMA system, whose performance will no longer be interference-limited, for its application in futuristic wireless communications. To achieve this, many challenging issues should be tackled, such as innovated design approaches for CDMA codes, multi-dimensional spreading techniques, suitable CDMA signaling format for high-speed bursty traffic, and so forth. This chapter will review the author’s ongoing research activities on the NG-CDMA technology, which can offer a performance never inferior to that of orthogonal frequency division multiple access (OFDMA) technology. In particular, the author will briefly introduce a new CDMA code design method, called Real Environment Adapted Linearization (REAL) approach, which can be used to generate CDMA code sets with inherent immunity against multipath interference and multiple access interference for both uplink and downlink transmissions. The chapter will also illustrate that an interference-free CDMA can only be made possible with the application of orthogonal complementary codes (OCCs). The use of traditional CDMA codes, such as Gold, Kasami, Walsh-Hadamard and OVSF codes, all working on an one-code-per-channel basis, will never help in this sense. Several other topics related to the NG-CDMA technology will also be addressed, such as system performance issues, other properties of the NG-CDMA technology, and so on. DOI: 10.4018/978-1-61350-101-6.ch805
3 citations
TL;DR: The results indicate that on a nondispersive radio channel with a path loss that is proportional to the fourth power of the distance, the interuser interference is approximately 10 dB higher in CDMA than in TDMA, which may seem surprising.
Abstract: We investigate the interuser interference in cellular code-division multiple access (CDMA) and time-division multiple access (TDMA) systems and compare the two multiple access techniques at different levels of user density per cell. The study includes the interference both on the downstream channel (from base station to users) and on the upstream channel (from users to base station). The purpose is to compare the two multiple access techniques when the total bandwidth occupancy and the maximum number of users per cell are the same. The results indicate that on a nondispersive radio channel with a path loss that is proportional to the fourth power of the distance, the interuser interference is approximately 10 dB higher in CDMA. The implication of this result, which holds for both the downstream and the upstream channels, is that for the same total bandwidth and number of users per cell, TDMA gives substantially superior bit error rate (BER) performance. This is confirmed by our numerical results evaluated for both additive white Gaussian noise (AWGN) channels and memoryless flat Rayleigh fading channels. Alternatively, CDMA needs approximately 10 times more bandwidth to achieve the same signal-to-interference (S/I) ratio, a result which may seem surprising, because the fact that CDMA employs a frequency reuse factor of 1 is often given as an evidence that this technique can support a higher number of users than TDMA in a given geographic area and frequency bandwidth.
3 citations
References
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18 Jun 1995
TL;DR: It is pointed out that multidimensional modulation systems essentially have the same performance and bandwidth efficiency as conventional 2-D systems.
Abstract: The paper presents a generalization of multidimensional modulation to all dimensions that are an integer power of 2. Minimum-bandwidth transfer functions are constructed using binary orthogonal Walsh-Hadamard sequences. The author also presents a time-domain approach which consists of using Walsh-Hadamard sequences as spreading and despreading sequences and discusses its relationship with conventional direct sequence code-division multiple access (DS/CDMA). It is pointed out that multidimensional modulation systems essentially have the same performance and bandwidth efficiency as conventional 2-D systems.
13 citations
Additional excerpts
...As it was noted in [ 4 ], OCDMA is a particular form of multidimensional modulation which does not offer any increase of the spectral efficiency with respect to 2-D signaling....
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