S. Ulukus and R. D. Yates, "Iterative construction of optimum signature sequence sets in synchronous CDMA systems," IEEE Trans. Inform. Theory, vol. 47, no. 5, pp. 1989.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....life in mobile stations. Until recently, power control and codeword adaptation were treated as distinct problems, with researchers concentrating on either transmitter power control [2] 10] 11] 19] or spectrum utilization through signal design for efficient multiple access [4] 7] 9] [13], 15] 16] In the traditional approach transmitted power is regulated to provide each user with an acceptable connection by limiting the interference caused by other users, and the power control problem requires that a vector of users transmitter powers be computed such that a specified set ....

....the design of signature sequences (codewords) or waveforms to be used by users in a CDMA system such that a given criterion is optimized. This can be an individual criterion that defines performance or quality of service achieved by a given user like the signal to interference ratio [7] 8] [13] or the required signal bandwidth [4] 15] or a global criterion like sum capacity or total squared correlation [9] 17] 18] Algorithms for signal design can be either centralized, in which case optimal signatures are computed at the base station receiver and then assigned to users [4] 9] ....

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S. Ulukus and R. Yates. Iterative Construction of Optimum Signature Sequence Sets in Synchronous CDMA Systems. IEEE Transactions on Information Theory, 47(5):1989.

....a code division multiple access (CDMA) system, the authors of [1] present a combinatorial algorithm to generate a set of signature sequences that achieves the maximum sum capacity. These sets also minimize a performance measure called generalized total square correlation (TSC ) Ulukus and Yates [2] propose an iterative algorithm suitable for distributed implementation: at each step, one signature sequence is replaced by its linear minimum mean square error (MMSE) filter. This algorithm results in a decrease of TSC at each step. The MMSE iteration has fixed points not only at the optimal ....

....by its linear minimum mean square error (MMSE) filter. This algorithm results in a decrease of TSC at each step. The MMSE iteration has fixed points not only at the optimal configurations which attain the global minimum TSC but also at other configurations which are suboptimal. The authors of [2] claim that simulations show that when starting with random sequences, the algorithm converges to optimum sets of sequences, but they give no formal proof. We show that the TSC function has no local minima, in the sense that given any suboptimal set of sequences, there exist arbitrarily close ....

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S. Ulukus and R. Yates, "Iterative construction of optimum signature sequence sets in synchronous CDMA systems," IEEE Trans. Inform. Theory, vol. 47, pp. 1989.

.... achieve the Welch lower bound on the sum of squared coefficients of the cor relation matrix or equivalently STS = I [18] An iterative centralized construction procedure for WBE sequences was given in [19] A simple decentralized construction procedure for WBE sequences was presented in [60] and later analyzed for more general framework in [61] In the case that some users have oversized powers, they are assigned orthogonal sequences and there is an explicit loss in sum capacity compared to the case of the Gaussian multiple access channel GMAC (Theorem 3.1 in [19] However, as ....

....the set of indices Gi of the users in group i (i = 1, r) The validation of this statement is that the if implication follows by substituting the sequence matrix of group orthogonal sequences S T = S, S] in (1.8) and the only if directly from [191. A similar conclusion was derived in [60] for unit energy sequences with equal received user powers. In practice, for an arbitrary distribution of user powers, it is not always possible to divide users in groups with exactly equal total power per group. The following equation quantifies the exact loss in sum capacity for the case of ....

[Article contains additional citation context not shown here]

S. Ulukus and R. D. Yates, "Iterative construction of optimum signature se- quence sets in synchronous CDMA systems," IEEE Trans. on Inform. Theory, pp. 1989.

....achieve the Welch lower bound on the sum of squared coefficients of the correlation matrix or equivalently c [11] An iterative centralized construction procedure for WBE sequences was aaT I . given in [8] A simple decentralized construction procedure for WBE sequences was pre sented in [6] and later analyzed for more general framework in [7] In the case that some users have oversized powers, they are assigned orthogonal sequences and there is an explicit loss in sum capacity compared to the case of Gaussian multiple access channel (Theorem 3.1 in [8] However, as will be ....

.... P to the set of indices Gi of the users in group i (i = 1, r) The validation of this statement is that the if implication follows by substituting the sequence matrix of group orthogonal sequences S = S, St] in (3) and the only iF directly from [8] A similar conclusion was derived in [6] for unit energy sequences with equal received user powers. 11 In practice, for an arbitrary distribution of user powers, it is not always possible to divide users in groups with exactly equal total power per group. The following equation, derived in Appendix B, quantifies the exact loss in sum ....

S. Ulukus, R.D. Yates, 'Iterative Construction of Optimum Signature Sequence Sets in Synchronous CDMA Systems', IEEE Trans. on Inform. Theory, vol.47, pp. 1989-1998, July 2001.

.... signatures [2] Of interest in this paper are the class of quasi orthogonal signature sequences known as Welch bound equality (WBE) sets since they are sum capacity optimal [3] see also [4] and the references therein) Algorithms for finding general WBE signature sets have appeared recently in [5] and [6] The optimality of WBE signature sets when minimum mean squared error (MMSE) decoding is used at the receiver for the uplink and downlink cases and a variety of power control strategies was derived in [7] Unfortunately, as mentioned in [4] and proven herein, WBE sequence sets in general ....

....different lengths of spreading sequences. Examples along these lines are available in [8, 1, 2] 3. 3 WBE Sequences Recently many researchers have pointed out the importance of constructing quasi orthogonal signature sets for synchronous CDMA that satisfy the Welch bound with equality, see e.g. [3, 4, 5, 6]. Recall that the Welch bound provides a lower bound on the sum of the squared correlations for a set of N signature sequences s k in C [9] i.e. A(S) # . 6) 6 Sequences that satisfy this bound with equality are called Welch bound equality sequences. A necessary and sufficient condition ....

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Sennur Ulukus and Roy D. Yates, "Iterative construction of optimum signature sequence sets in synchronous CDMA systems," IEEE Trans. Inform. Theory, vol. 47, no. 5, pp. 1989.

.... # is such that ## # # ## then the vector # # # # is such that # ## # # # # ## ## and thus that all the nonvanishing eigenvalue of ## and # coincide so that # # ### ### # ###### # (2) Such a property has been already exploited in the context of synchronous DS CDMA [13] and we here take advantage of it noting that it helps changing an expression dealing with the sampling of cross correlation terms (## ) into an expression entailing the computation of auto correlation terms (# #) Such a change in point of view has a twofold consequence. As a first remark, ....

S. Ulukus, R.D. Yates, "Iterative Construction of Optimum Signature Sequence Sets in Synchronous CDMA systems," IEEE TRANSAC- TIONS ON INFORMATION THEORY, vol. 47, pp. 1989-1998, 2001

....procedure. 3 Interference Avoidance: A Brief Review Interference avoidance methods allow users in a multiaccess system to adapt their transmitted signals to achieve better performance by maximizing signal to interference plus noiseratio. Introduced originally in the context of DS CDMA systems [8, 9] interference avoidance methods have been subsequently developed [6] in a more general signal space formulation. The framework for interference avoidance presented in [6] assumes an arbitrary N dimensional signal space for the receiver and all users in the multiuser system, as opposed to the ....

S. Ulukus and R. Yates. Iterative Construction of Optimum Signature Sequence Sets in Synchronous CDMA Systems. IEEE Transactions on Information Theory, 47(5), July 2001.

....channel autocorrelation (codewords) for transmission of each bit, and by defining an equivalent clear space problem for the given user. Formulation of this equivalent problem allows Popescu and Rose: Multiaccess Dispersive Channels and IA 3 direct application of interference avoidance techniques [21, 23] to determine optimal codewords for each bit, since it has been shown that interference avoidance always produces sum capacity maximizing codeword ensembles [1, 19, 20] Furthermore, the resulting codeword sets maximize ensemble SINR and hence user capacity [26, 27] The simplest multiple user ....

....of codewords. However, we instead pursue the alternate approach of codeword optimization that will allow the use of simple matched filters as optimal linear receivers. 3. 2 Interference Avoidance To generate such optimal signal sets, a class of interference avoidance algorithms has been proposed [21, 23] in which the signature waveform of a given user is adapted to minimize interference from other users and achieve maximum signal to interference ratio. It has been proven [1, 20] that this procedure will always yield an optimal signal set. We will use the greedy eigen algorithm [20,21] in the ....

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S. Ulukus and R. Yates. Iterative Construction of Optimum Signature Sequence Sets in Synchronous CDMA Systems. IEEE Transactions on Information Theory, 47(5), July 2001.

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S. Ulukus and R. D. Yates, "Iterative construction of optimum signature sequence sets in synchronous CDMA systems," IEEE Trans. Inform. Theory, vol. 47, no. 5, pp. 1989.

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S. Ulukus and R. D. Yates, "Iterative construction of optimum signature sequence sets in synchronous CDMA systems," IEEE Trans. IT, vol. 47, no. 5, pp. 1989.

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S. Ulukus and R. D. Yates, "Iterative construction of optimum signature sequence sets in synchronous CDMA systems," IEEE Trans. Inform. Theory, vol. 47, no. 5, pp. 1989.

No context found.

S. Ulukus and R. D. Yates, "Iterative construction of optimum signature sequence sets in synchronous CDMA systems," IEEE Trans. Inform. Theory, vol. 47, no. 5, pp. 1989.

No context found.

Sennur Ulukus and Roy D. Yates, "Iterative construction of optimum signature sequence sets in synchronous CDMA systems," IEEE Trans. IT, vol. 47, no. 5, pp. 1989.

No context found.

S. Ulukus and R. D. Yates, "Iterative construction of optimum signature sequence sets in synchronous CDMA systems," IEEE Trans. Inform. Theory, vol. 47, no. 5, pp. 1989.

No context found.

S. Ulukus and R. D. Yates, "Iterative construction of optimum signature sequence sets in synchronous CDMA systems," IEEE Trans. on Inform. Theory, vol. 47, no. 5, pp. 1989.

No context found.

S. Ulukus and R. Yates, "Iterative construction of optimum signature sequence sets in synchronous cdma systems," IEEE Transactions on Information Theory, vol. 47, no. 5, July 2001.

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S. Ulukus and R. D. Yates. Iterative construction of optimum signature sequence sets in synchronous CDMA systems. IEEE Trans. Info. Theory, 47(5):1989.

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