Multiple access using two sets of orthogonal signal waveforms

Int J Wireless Inf Networks

2010

One of the efficient schemes to overload a CDMA system is to use two sets of orthogonal signal waveforms (O/O) Sari, Vanhaverbeke and Moeneclaey, IEEE Communication Magazine, 56-59, 2000. In this paper, we have presented the analysis of hard decision interference cancellation (HDIC) receiver for O/O overloaded DS-CDMA system. A closed form expression for the average bit error rate (BER) is obtained, for each stage of HDIC receiver, without considering the correlation between the multiple access interference and Gaussian noise. It is observed that at lower overloadings, analytical result matches closely to that obtained from simulation. But there is a difference between two at higher overloadings. The reason for such a difference is the inaccuracy in variance calculation due to the assumption of zero correlation. By using the Price's theorem, we have obtained the correlation between tentative data decision and Gaussian noise samples. The overloading performance of a specific Quasi-synchronous sequence (QOS) O/O scheme is also evaluated using interference cancellation receivers.

Section: Introductionmentioning

confidence: 99%

An Analytical Model of Iterative Interference Cancellation Receiver for Orthogonal/Orthogonal Overloaded DS-CDMA System

Int J Wireless Inf Networks

2010

“…For instance, the first set is assigned to the N users and the second set is assigned to the additional M users [3], hybrid TDMA/OCDMA [4] and quasiorthogonal sequences (QOS) [5] which is a part of cdma2000 standard. In random O/O (s-O/O), first set of N users are assigned Walsh-Hadamard (WH) orthogonal codes overlaid by the same PN scrambling sequence.…”

Section: Introductionmentioning

confidence: 99%

BER Analysis of Hard Decision Interference Cancellation Receiver for Overloaded DS-CDMA System

2008 IEEE Sarnoff Symposium

2008

Overloaded Code Division Multiple Access (CDMA) system accommodates more number of users than the spreading factor, N. One of the efficient scheme to overload a CDMA system is to use two sets of orthogonal signal waveforms (O/O). The first set is assigned to the N users and the second set is assigned to the additional users. An iterative multistage detection technique is used to cancel interference between the two sets of users. In this paper, we have presented the analysis of HDIC receiver for O/O overloaded DS-CDMA system. A closed form expression for the average Bit Error Rate (BER) is obtained, for each stage of HDIC receiver, without considering the correlation between the multiple access interference and Gaussian noise. The analytical results as obtained from the closed form expression are compared with simulation results for quasi orthogonal sequence (QOS) O/O overloading schemeproposed for cdma2000. It is observed that at lower overloadings, analytical result matches closely to that obtained from simulation. But there is a difference between two at higher overloadings. The reason for such a difference is the inaccuracy in variance calculation due to the invalid assumption that the interference from different users and Gaussian noise are mutually uncorrelated. By taking the correlation into account and employing Price's theorem, an improved BER expression is obtained.

“…Specific examples of 0/0 are scrambled O/O(s-O/O) [2], Overall permuted 0/0 (o-O/0) [3], Hybrid TDMA/OCDMA [4] and quasi-orthogonal sequences (QOS) [5], that are part of cdma2000 standard. These schemes required perfect time alignment of the different users which is generally achieved in the down link.…”

Section: Introductionmentioning

confidence: 99%

Performance Evaluation of Orthogonal/Scrambled-Orthogonal Overloaded DS-CDMA System

Ramesh²,

2007 IFIP International Conference on Wireless and Optical Communications Networks

2007

Overloading is a bandwidth efficient scheme to accommodate more number of users than the spreading factor, N in a DS-CDMA system. In this paper, the performance of an overloading scheme in which the first N users are assigned WalshHadamard orthogonal codes and extra users are assigned the same WH codes but overlaid by a common scrambling sequence is evaluated. The allowable load of this scheme is investigated, so that the uncoded performance with iterative multistage interference cancellation detector using hard (HDIC) and soft (SDIC) decision functions remains close to the single user bound. It is shown that this scheme provides 19% and 11% overloading with SDIC technique for N= 16 and 64 respectively.