Capacity Improvement in CDMA Downlink With Orthogonal Code-Hopping Multiplexing

Abstract

Orthogonal code-hopping multiplexing (OCHM) is a statistical multiplexing scheme designed to increase the number of allowable downlink channels in code division multiple access (CDMA) systems. OCHM is expected to compensate for a lack of codewords in future communication systems. In CDMA systems including OCHM, system capacity is limited by the number of codewords and power (or interference), and the maximum system capacity is determined by a stronger limitation between them. Call blockings due to power limitation may occur firstly if downlink channels demand large E b /I 0 values and a high-channel activity. On the other hand, code limitation may occur prior to power limitation in CDMA. The maximum system capacities determined by both code and power limitations must be known, even in OCHM. However, previous studies on OCHM system capacity focused only on increasing the number of multiplexed users with no consideration of the power limitation. In this paper, the overall system capacity of OCHM considering both code and power limitations was evaluated. For this analysis, the transmission chip energy of base station (BS) and inner/outer-cell interference is mathematically derived in a multicell and multiuser environment. The downlink system capacity for OCHM is larger than for orthogonal code division multiplexing (OCDM) as other cell interference (OCI), mean channel activity, and the required E b /I 0 value decrease. Index Terms-Code division multiple access (CDMA), downlink capacity, orthogonal code-hopping multiplexing (OCHM), perforation, synergy. I. INTRODUCTION P ACKET-TYPE services, such as hypertext transfer protocol (HTTP), file transfer protocol (FTP), and wireless application protocol (WAP), have gradually increased and may become dominant in future wireless communications. In contrast to voice traffic, which is a major service in 2G, these packet-based services have two different characteristics. First, they exhibit high burstiness with low activity and second,

Performance Analysis of Orthogonal Code Hopping Multiplexing Systems

“…Recently, we have analyzed the downlink user capacity of OCHM system and have compared it with the user capacity of the conventional CDMA system [6]. In [6], we defined code and power capacities independently like as the conventional CDMA systems. Thus, the overall user capacity is derived by the minimum value of two capacities.…”

“…In [6], we have illustrated the user capacity which is the minimum value of Eqs. (23) computer simulations for several cases in [6]. However, as we noted in Section III-C, the additional required energy at MU increases as P p increases.…”

“…Table II summarizes the parameters and the overall user capacities of OCHM systems for varying the OCI values. The other parameters for modelling interference have the same values as those used in [6] and we assume that an omni-antenna is used at BS. When the OCI value is set to 20%, 281 users can be accommodated in downlink, which is much larger than the number of orthogonal codewords (N oc = 64).…”

Advanced handover scheme considering downlink and uplink service traffic in asymmetric channel

“…However, the difference between the uplink and downlink is not mentioned. In [10], Moon et al propose a downlink model considering geometric information and the intercell interference. However, the main interest of [10] is to model a downlink channel of code division multiple access (CDMA) systems, and neither the channel symmetry nor the correlation between the downlink and uplink are mentioned.…”

“…In [10], Moon et al propose a downlink model considering geometric information and the intercell interference. However, the main interest of [10] is to model a downlink channel of code division multiple access (CDMA) systems, and neither the channel symmetry nor the correlation between the downlink and uplink are mentioned. The link model in [11] is considered a downlink and uplink signal-to-interferenceplus-noise ratio (SINR) in an OFDMA system.…”