New adaptive bit allocation algorithms for multiuser OFDM/CDMA systems

Abstract

An adaptive bit allocation algorithm is proposed for multiuser transmission in OFDM/CDMA systems. The proposed scheme takes advantage of frequency diversity to dynamically allocate a suitable number of bits/per symbol on subcarriers of each user based on the transmitting objectives such as the required transmission rate and BER. A suboptimal solution to the problem of the bit allocation on subcarriers for each user is derived by minimizing the interference power from each user. Then an algorithm for adjusting the number of allocated bits is used to further reduce the interference without changing the total transmitted data rate. The performance obtained by minimizing the interference resulting from each user is studied in terms of BER, transmission data rate and the system capacity supporting multiple users. The theoretical analysis and simulation results show that the proposed algorithm substantially outperforms those reported previously.

Ultra wideband indoor positioning system in support of emergency evacuation

“…A new algorithm of adaptive subcarrier allocation and bit loading (A-SABL) [6,7,11] was developed for simultaneous transmission of both the position tracking information data and the communication data using OFDM/CDMA mechanism over ultra wideband channels. This algorithm takes advantage of the frequency diversity to dynamically assign the number of subcarriers and bits/per symbol on each subcarrier in Orthogonal Frequency Division Multiplexing (OFDM) according to the transmission requirements, meanwhile, all mobile agents can access all available subcarriers using Code Division Multiple Access (CDMA) technique.…”

“…CDMA combined with OFDM using space-time coding techniques and multiple input multiple output (MIMO) antenna is able to provide the multiuser access capability by transmitting and receiving of multiple tasks simultaneously over UWB channels [6,7,11] in the same frequency band, so that this CDMA/OFDM system can be integrated using one single UWB chipset. Based on the estimation of channel quality in terms of instantaneous subcarriers gains [6,11], subcarrier with suitable bit load is dynamically allocated to each transmission task according to quality of service (QoS) requirements.…”