Efficient packet data service in a spread spectrum OFDM cellular system with 2‐dimensional radio resource allocation

Abstract

SUMMARYThis paper describes and evaluates a novel 2-dimensional radio resource allocation scheme for highthroughput cellular packet data access. The proposed system employs spread spectrum orthogonal frequency division multiplexing with adaptive time and frequency allocation (SS-OFDM-F/TA) of radio resources. In order to achieve high spectral efficiency of downlink packet transmissions to multiple mobile users, multi-user diversity available in the multi path fading environment is exploited through the use of adaptive modulation and coding, best serving sector selection, suitable scheduling of packet transmissions and hybrid ARQ employing soft-packet combining and incremental redundancy. The data throughput, packet delay and fairness of the system with slow and fast best sector selection are examined. A method of grouping disjoint sub-bands for use in highly frequency-selective environments is described and evaluated. Packet re-transmission options including a proposal of several asynchronous re-transmission algorithms and constraining the maximum re-transmission interval are also considered. It is demonstrated that the proposed spread spectrum OFDM system is capable of reaching a spectral efficiency of about 1.7 b/sec/Hz/ sector with single receive and transmit antennas, and seems to provide a promising solution for highthroughput best-effort delay-tolerant data services in future cellular radio systems.

Diversity Combining Options and Low-Complexity MMSE Equalization for Spread Spectrum OFDM Systems in Frequency Selective Fading Channels

“…It can be noted that the accuracy of the analytical expression for the BER found by using (30) in (12) with T p = 1 (partially loaded system with no diversity), can be evaluated from Figures 4 and 5 if T is replaced by L / K.…”

“…Again, (21)-(23) can substituted into (6) (with μ A replaced by μ A,T , μ B replaced by μ B,T , and σ 2 A replaced by σ 2 A,T ), and subsequently (12) to give a closed form expression for the BER with QPSK modulation. This type of chip-level combining is analogous to using longer spreading sequences and MMSE equalization per spreading sequence as described by (4), but it is much simpler (see Section 3.3 for further discussion).…”

“…, and subsequently into (12) to give an analytical expression for the BER with QPSK modulation. In this expression, 1/λ is the SINR per diversity replica.…”

“…Concatenation of orthogonal and pseudo-noise spreading helps mitigate inter-cell interference. Due to its beneficial properties, SS-OFDM has been proposed for packet data service on the cellular downlink [10][11][12].…”

Multi-sub-channels Spread Spectrum Anti-interference System and its Performance

“…The combination of spread spectrum technology and OFDM technology could provide a more reliable SS-OFDM communication link [11][12][13][14]. Most of the related studies only directly apply spread spectrum methods to OFDM, which mainly embarks on how to improve the BER performance of transmission signal under multipath interference or other non-anthropogenic interferences, with the absence of anthropogenic interferences.…”