Browse Prior Art Database

Code Selection Criterion for MC-CDMA with Multi-code Transmission

IP.com Disclosure Number: IPCOM000029049D
Original Publication Date: 2004-Jun-14
Included in the Prior Art Database: 2004-Jun-14
Document File: 5 page(s) / 103K

Publishing Venue

Motorola

Related People

Hiroshi Hayashi: AUTHOR

Abstract

In this document, a code selection criterion using minimum despreading factor (MDF) is proposed for multi-carrier code division multiple access (MC-CDMA) with multi-code transmission. The proposed criterion provides high signal to interference and noise power ratio (SINR) for both one-dimensional and two-dimensional spreading in MC-CDMA.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 40% of the total text.

Code Selection Criterion for MC-CDMA with Multi-code Transmission

Hiroshi Hayashi

Abstract

In this document, a code selection criterion using minimum despreading factor (MDF) is proposed for multi-carrier code division multiple access (MC-CDMA) with multi-code transmission. The proposed criterion provides high signal to interference and noise power ratio (SINR) for both one-dimensional and two-dimensional spreading in MC-CDMA.

1                    Background

For MC-CDMA with multi-code transmission, Walsh code is typically used as the spreading codes. The number of available codes is equal to the spreading factor. In fully loaded case, all the available codes are used to multiplex maximum number of the code channels. However, in fractionally loaded case, a subset of the codes is selected from the entire available codes. In MC-CDMA, time or frequency selectivity due to the multi-path fading propagation distorts orthogonality among code channels and brings about inter-code interference. The code selection (which the active codes are selected) affects the amount of inter-code interference, and impacts the error rate performance. In order to reduce the inter-code interference, the code selection criteria were proposed by D. Mottier, D. Castelain [1] and S. Qinghua, M. Latva-aho [2].

When K active codes are selected from N available codes (K< N) by using criterion [2], the available codes are arranged in ascending order of zero crossing number, and code index n (n=0,1,2,...N-1) is assigned to each of the arranged codes. The arranged codes with index #0 and index #N-1 are selected for active codes with index #0 and index #K-1, respectively. Then the rest of the K-2 arranged codes are selected that index of the selected K-2 codes are distributed as equally as possible.

In criterion [1], a hypothetical subset of the spreading codes is extracted from the entire available codes, and the hypothesis is evaluated by using a cost function. The evaluation is repeated for all the possible subsets, and then the optimal subset with the minimal cost are selected by the criterion.

2                    Problems to be solved

By using criterion [1], Signal to Interference and Noise power Ratio (SINR) is severely degraded for large number of active codes. It is because criterion [1] does not restrict the code selection, when the number of active codes is more than half of the spreading factor.

By using criterion [2], the code selection is restricted so tightly that only one combination satisfies the criterion. Only the number of active codes determines the selected codes. Therefore, reallocation of spreading codes is required, whenever the number of active codes was changed.

Moreover, using either criterion [1] or criterion [2] degrades SINR for two-dimensional spreading [3][4]. It is because only one-dimensional (time or frequency) spreading is considered by both criteria.

3                    Embodiment

In order to resolve the problems, a new code selection criterion using minimum despreading factor (MDF criterion) is p...