On the Construction of Orthogonal Spreading Code Groups for MC-CDMA with FDE in a Frequency Selective Channel

Adachi, Kôichi; Nakagawa, Masao

doi:10.1587/transcom.e93.b.650

Cited by 1 publication

(2 citation statements)

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“…The advantage is that the MC-CDMA architecture is not modified and a minimum amount of computation, which can use simple single-user detection (SUD), is required at the receiver. The issue is then to find the best spreading code families in a statistical sense [12][13][14][15][16][17] and the optimal set of codes to assign to the active users for a given family [18][19][20][21][22][23][24][25].…”

Section: Introductionmentioning

confidence: 99%

“…The drawback is that the maximum size of this set is the ratio between the number of subcarriers and the channel length, which limits the number of MAI free users as in [10]. According to [25], this number is also influenced by the distribution of time delay differences among the channel paths. In [23], CSI is estimated by the simple least squares method, and then an iterative procedure is used to select the code set that minimizes the total MAI.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Spreading code allocation strategy for downlink multicarrier code division multiple access transmission in a correlated Rayleigh fading channel

Garnier

Delignon

Ghazi

et al. 2012

Wirel. Commun. Mob. Comput.

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In this paper, we address the problem of multiple access interference (MAI) in a downlink multicarrier code division multiple access system. Because in the realistic case of correlated faded subcarriers, MAI greatly depends on the codes assigned to users, one way of improving performance without increasing receiver complexity consists in an appropriate code selection. We propose a code allocation strategy with the following properties: possible use with any code sequence and equalizer, low complexity, and efficient management of load variations. The allocation problem is formulated as a minimization problem of a cost function related to MAI. First, we provide analytical expressions for the channel frequency correlation function after maximum ratio combining, equal gain combining, and minimum mean square error equalization and for the MAI power. Then, by approximating these expressions, we define a simple cost function and build an iterative algorithm on the basis of the minimum maximum criterion to select the spreading codes. Finally, a complete analysis of the allocation efficiency is provided versus key parameters, in particular, the degree of correlation between the faded subcarriers, the system load, and the equalization techniques.

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