Collision Mitigation by Log-Likelihood Ratio (LLR) Conversion in Orthogonal Code-Hopping Multiplexing

IEEE Trans. Wireless Commun.

2007

Beyond-3G wireless communication systems should support packet traffic with both low/medium rate and high rate services. Scheduling-based resource allocation schemes may cause a problem in accommodating low/medium rate services due to a rate mismatch and a large signaling overhead. Dedicated resource allocation/multiplexing schemes are also inadequate for accommodating packet-type traffic that is characterized by low channel activity and high burstiness. Therefore, we propose a new orthogonal frequency and code hopping multiplexing (OFCHM) scheme for downlink multiplexing to provide efficient support of packet traffic with low/medium data rates in a spread OFDM environment. The performance of the proposed scheme is evaluated in terms of the statistical multiplexing gain, the block error rate, and the overall capacity by using both an analytical approach and simulation. The proposed scheme yields a larger overall downlink capacity than a dedicated resource allocation/multiplexing scheme. A comparison study with the variable spreading factor-orthogonal frequency and code division multiplexing (VSF-OFCDM) system through system-level simulations is also performed. The comparison results show that the OFCHM system yields better performance than the VSF-OFCDM system in packet delay, packet delay variance, and fairness, and has a system throughput advantage with low/medium rate services.Index Terms-OFDM, spread OFDM, multiplexing, orthogonal frequency and code hopping multiplexing, variable spreading factor-orthogonal frequency and code division multiplexing (VSF-OFCDM).

Section: Introductionmentioning

confidence: 99%

Performance Analysis of Orthogonal Frequency and Code Hopping Multiplexing

Moon

Kim

IEEE Trans. Wireless Commun.

2007

“…Statistically, the users near BS have a more energy gain than those at the cell boundary. Therefore, in OCHM systems, the energy gain at the receiver due to the synergy scheme is complex to analyze even though several previous papers assumed all the HP-collision users are located in the same distance from BS in their performance evaluations [3]- [7].…”

Section: A Ochm Mechanism Hp Collisions Perforation and Synergymentioning

confidence: 99%

“…An orthogonal code hopping multiplexing (OCHM) system [3]- [7] has been proposed to accommodate a lager number of mobile users (MUs) with bursty traffic than the number of orthogonal codewords in downlink. It utilizes statistical multiplexing for orthogonal downlink in DS/CDMA systems.…”

Section: Introductionmentioning

confidence: 99%

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Performance Analysis of Orthogonal Code Hopping Multiplexing Systems

Jung

Jin

2006 IEEE International Conference on Communications

et al. 2006

Abstract-In orthogonal code hopping multiplexing (OCHM) systems, hopping pattern (HP) collisions may degrade the system performance. Previous studies on the effect of HP collisions in OCHM systems were mainly based on computer simulations and there was no rigorous mathematical analysis of bit error rate (BER) performance. The HP collisions in OCHM systems differ from the hits in frequency-hopping (FH) systems or intracell interference in DS-CDMA systems because it can be effectively controlled through synergy and perforation techniques. In this paper, we introduce a received signal model for OCHM systems and analyze the BER performance for OCHM systems. Through the analysis of the BER performance, OCHM systems can be characterized more clearly and the allocated power at base station can be estimated. Furthermore, the user capacity is analyzed for a given channel coding scheme.

“…Multirate transmission for OCHM has been introduced [6], and OCHM capacity has been analyzed [7]. Channel coding at the OCHM receiver is important for the recovery of symbols lost due to code hopping, and the FER performance of OCHM has been evaluated [8], [9]. However, prior work has dealt with OCHM only for BPSK and QPSK modulations.…”

mentioning

confidence: 99%

Synergy/Perforation Control for 16-QAM in Orthogonal Code Hopping Multiplexing

Moon

Kwon

IEEE Trans. Veh. Technol.

2007

Orthogonal code hopping multiplexing (OCHM) is a statistical multiplexing scheme designed to accommodate a large number of allowable downlink channels in code division multiple access (CDMA) systems. However, OCHM may yield a worse bit error rate (BER) performance than the conventional CDMA systems due to code collisions. Therefore, a synergy/perforation operation, which is a control scheme for mapping code-colliding modulation symbols to specific constellation points on the I-Q plane, is needed to compensate for BER degradation, and this synergy/perforation operation should be defined separately with modulation types. Previously, synergy/perforation control schemes for quadrature phase shift keying (QPSK) and binary phase-shift keying (BPSK) have been proposed, but there has been no study of 16-quadratic-amplitude modulation (16-QAM) in OCHM. We propose two synergy/perforation control schemes for 16-QAM in OCHM and a log-likelihood ratio conversion scheme for 16-QAM in OCHM. The proposed control schemes are evaluated by an analytical approach and simulations and are compared to the previous scheme for QPSK modulation. We show that the proposed control scheme has a performance similar to that of QPSK modulation in terms of the mean synergy ratio for code-colliding modulation symbols and additional required E b /N 0 .