OFDM and OFDMA Communication Systems

Orthogonal frequency division multiplexing(OFDM) is an attractive technique for combating the effects of delay spread in high-speed wireless data transmission. By transmitting multiple data streams in parallel over different low-rate subchannels, intersymbol interference (ISI) can be reduced significantly. If each subchannel is narrow enough such that the multipath fading can be characterized as flat, the need for equalization can be eliminated. The popularity of OFDM is evident by its use in recent standards for digital audio and video broadcasting(DAB/DVB), asymmetric digital subscriber line (ADSL), and wireless local area network (WLAN)applications.

Selected papers

P. Svedman, S.K. Wilson, L.J. Cimini, and B. Ottersten, “Opportunistic Beamforming and Scheduling for OFDMA Systems,” IEEE Trans. on Commun., May 2007, pp. 941-952.

S. Ye, R.S. Blum, and L.J. Cimini, “Adaptive OFDM Systems with Imperfect Channel State Information,” IEEE Trans. on Wireless Commun., Nov. 2006, pp. 3255-3265.

MIMO Communication

Multiple-input multiple-output(MIMO) technologies have evolved to become an inherent component in all next-generation wireless systems. MIMO technologies will be a part of wireless standards including the cellular systems EV-DO Rev C, UMTS LTE, and the IEEE 802.xx family of standards 802.16e, 802.16j, 802.16m, and 802.11n. Future enhancements to these standards, such as those proposed for the IMT Advanced concept, will use MIMO to achieve required data rates in the order of hundreds of Mbps and spectral efficiencies in the order of tens of bps/Hz.

Selected papers

Y. Li, L. Zhang, L.J. Cimini, and H. Zhang, “Statistical Analysis of MIMO Beamforming With Co-Channel Unequal-Power MIMO Interferers Under Path-Loss and Rayleigh Fading,” IEEE Trans. on Signal Proc., Aug. 2011, pp. 3738-3748.

Cooperative Communication

Cooperative diversity is a set of techniques that exploits the spatial diversity available among a collection of distributed single-antenna terminals. A two-stage relaying strategy has been used in most proposed cooperative systems. In the first stage, a source transmits and all the other nodes listen; in the second stage, the relays cooperate to retransmit the source message to the destination. Several relay management strategies have also been devised. In selective decodeand-forward relaying, a node is called a decoded node if it can correctly decode the source message; then, some subset of the decoded nodes is selected to forward the source message to the destination.

Selected papers

L. Zhang and L.J. Cimini, “Efficient power allocation for decentralized distributed space-time block coding,” IEEE Trans. on Wireless Commun., Mar. 2009, pp. 1102-1106.

Energy-Efficient Wireless Communication

Energy efficiency is defined as the number of transmitted information bits per unit energy, which has been studied recently and which is becoming increasingly important for wireless communication systems.

Selected papers

Jiang and Cimini, “Antenna Selection for Energy-Efficient MIMO Transmission,” IEEE Wireless Commun. Letts., Dec. 2012, pp. 577-580.

Lim and Cimini, “Energy-Efficient Cooperative Relaying in Heterogeneous Radio Access Networks,” IEEE Wireless Commun. Letts., Oct. 2012, pp. 476-479.