On the radio capacity of TDMA and CDMA for broadband wireless packet communications

• Published in: IEEE transactions on vehicular technology Vol. 52; no. 1; pp. 60 - 70
• Main Authors: Krishnamurthy, S.V., Acampora, A.S., Zorzi, M.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.01.2003; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Broadband; Broadband communication; Cellular; Circuits; Code division multiple access; Delay; Equipments and installations; Exact sciences and technology; Fading; Information, signal and communications theory; Interchannel interference; Mobile radiocommunication systems; Multiaccess communication; Multiple access interference; Multiplexing; Power control; Radio; Radiocommunications; Signal and communications theory; Spreads; Telecommunications; Telecommunications and information theory; Telephony; Time division multiple access; Wireless communication; Wireless networks; Performance evaluation; Mobile radiocommunication; packet communications; Packet switching; TDMA; Wireless telecommunication; quality-of-service (QoS); code-division multiple access (CDMA); Wide band transmission; Cell network; Signal to interference ratio; Multiuser channels; Time division multiple access; Capacity; Code division multiple access; Delay time; Service quality
• DOI: 10.1109/TVT.2002.807230
• ISSN: 0018-9545

Studies of the capacity of cellular systems, stated in terms of the admissible number of remote users, have generally been limited to voice telephony. We address the problem of comparing the interference-limited performance of code-division multiple-access (CDMA) and time-division multiple-access (TDMA) systems in a packet-switched environment. The objective is to determine whether the capacity advantages claimed for circuit-switched CDMA still apply in a packet-switched environment, where the natural time diversity of bursty transmission may be a significant factor. Under a set of specific assumptions about the wireless environment (including path loss, shadow fading, multipath delay spread, cochannel interference, power control, and coding), we evaluate the number of users that can be admitted to the system while maintaining some desired quality-of-service (QoS) level. Four different classes of users with different characteristics and requirements are considered. The system capacity is found to depend significantly on the QoS objectives, which might be stated in terms of availability of some specified signal-to-interference level, packet-loss rate, or mean tolerable delay. The main finding is that strict requirements imposed on the radio access level tend to favor CDMA, whereas if some form of packet recovery is allowed at the higher layers (implying a relaxed set of requirements on the radio interface), then a somewhat higher capacity may be achieved by TDMA.