We developed a cross-layer design which combines adaptive modulation and coding at the physical layer with a truncated automatic repeat request protocol at the data link layer, in order to maximize spectral efficiency under prescribed delay and error performance constraints. We derive the achieved spectral efficiency in closed-form for transmissions over Nakagami-m block fading channels. Numerical results reveal that retransmissions at the data link layer relieve stringent error control requirements at the physical layer, and thereby enable considerable spectral efficiency gain. This gain is comparable with that offered by diversity, provided that the maximum number of transmissions per packet equals the diversity order. Diminishing returns on spectral efficiency, that result when increasing the maximum number of retransmissions, suggest that a small number of retransmissions offers a desirable delay-throughput tradeoff, in practice.
Bibliographical noteFunding Information:
Manuscript received December 5, 2002; revised March 16, 2003; accepted June 27, 2003. The editor coordinating the review of this paper and approving it for publication was H. Yanikomeroglu. This work was supported by the National Science Foundation under Grant 0105612, and by the Army Research Laboratory under the Collaborative Technology Alliance Program, Cooperative Agreement DAAD19-01-2-011. The material in this paper was presented in part at the IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC), pp. 110–114, Rome, Italy, June 15-18, 2003.
- Adaptive modulation and coding (AMC)
- Automatic repeat request (ARQ) protocol
- Cross-layer design
- Quality of service (QoS)
- Wireless networks