9:30, SPCOM-L5.1
ON THE PERFORMANCE OF MULTICARRIER CDMA USING MULTIPLE TRANSMITTERS
Q. SPENCER, A. SWINDLEHURST
Recent research has demonstrated the existence of transmission schemes and codes which provide diversity gain by using multiple transmitting antennas. This paper applies the concepts of multicarrier DS-CDMA systems to the multiple transmitter case. The multicarrier CDMA system discussed here was originally based on the assumption that the frequency-selective fading was uncorrelated from one subcarrier to the next. In this paper we derive the performance for a system whose subcarriers are subject to correlated fading, and the performance of a system partially or completely decorrelated by distributing the subcarriers across transmit antennas.

9:50, SPCOM-L5.2
JOINT TRANSMITTER / RECEIVER DESIGN FOR MULTICARRIER DATA TRANSMISSION WITH LOW LATENCY TIME
T. KARP, G. SCHULLER
In this paper a design method for low latency multicarrier transmission is presented. It can be considered as a gener­ alization of the Trailing­Zeros Transmitter approach in [1]. The generalization mainly consists of using FIR redundant filter banks for the transmitter and receiver instead of pure block transforms and allowing to choose the guard inter­ val independently of the channel impulse response length. Thanks to the latter, we can design a multicarrier transmis­ sion system with a low latency time, which is a critical pa­ rameter for online applications, even for the case that the channel has a long impulse response, as e.g. a twisted­pair copper wire line of several miles length. The design of the transmitter and receiver is based on a Smith decomposition of the channel. Advantages as well as limitations of the new algorithm are discussed. Web site: http://www.cvial.ttu.edu/~tkarp

10:10, SPCOM-L5.3
OPTIMAL TIME-FREQUENCY SIGNALING FOR RAPIDLY TIME-VARYING CHANNELS
T. KADOUS, K. LIU, A. SAYEED
We introduce a new signaling scheme for time- and frequency-selective channels that is a generalization of Multi-Carrier Code Division Multiple Access (MC-CDMA) signaling used in slowly time-varying channels. The Fourier basis functions used in conventional MC-CDMA systems encounter temporal distortion in rapidly time-varying channels resulting in degraded performance. The proposed scheme transmits the data over a set of orthonormal time-frequency basis functions whose time-frequency support is matched to the coherence time and bandwidth of the channel. The time-frequency signaling scheme approximately diagonalizes the time-varying multipath channel and each basis function encounters flat Rayleigh fading. We derive an optimal choice of basis parameters that yield the most accurate diagonalization for given multipath and Doppler spreads of the channel. The proposed system fully exploits the diversity afforded by the channel and delivers improved performance in rapidly time-varying channels in contrast to degraded performance of existing systems under such conditions.

10:30, SPCOM-L5.4
A MULTIRATE PILOT-SYMBOL-ASSISTED CHANNEL ESTIMATOR FOR OFDM TRANSMITTER DIVERSITY SYSTEMS
K. LEE, D. WILLIAMS
Orthogonal frequency division multiplexing (OFDM) transmitter diversity techniques have been shown to be efficient means of achieving near optimal diversity gain in frequency-selective fading channels. For these systems, knowledge of the channel parameters is required at the receivers for diversity combining and decoding. In this paper, we propose a low complexity, bandwidth efficient, pilot-symbol-assisted channel estimator for multiple transmitter OFDM systems. The pilot symbols are constructed to be non-overlapping in frequency to allow for the simultaneous sounding of the multiple channels. The time-varying channel responses are tracked by interpolating a set of estimates obtained through periodically transmitted pilot symbols. The effectiveness and limitations of the proposed estimator are verified by simulations.

10:50, SPCOM-L5.5
AN ALIAS-FREE ADAPTIVE EQUALIZER FOR OFDM SYSTEM
H. OCHI, T. MIYAGI
In this paper, we propose a subband adaptive digital filter (SBADF) for orthogonal frequency division multiplexing (OFDM) system. The proposed SBADF is able to carry out the exact system identification without the degradation effect of both the aliasing and the cross terms even under the critical sub-sampling. The inverse transfer function of the channel can be directly implemented after the system identification. The advantage of the proposed SBADF based equalizer is that it is not necessary to take into account of the delay in terms of transmission path because of the frequency-domain equalization. Some simulation results show the efficiency of the proposed SBADF for OFDM system.

11:10, SPCOM-L5.6
SPECIFICATION AND DESIGN OF A PROTOTYPE FILTER FOR FILTER BANK BASED MULTICARRIER TRANSMISSION
M. BELLANGER
The specifications of filter banks for multicarrier transmission systems with a large number of sub-channels are discussed, with application to xDSL and power line communication in mind. The near PR modulated approach is considered and the importance, for the system, of the prototype filter delay is stressed. An existing design technique, known to be particularly relevant to the context, is revisited from a frequency sampling perspective. The performance results in terms of sub-channel noise floor and delay are given for several filter lengths and an experimental validation is provided. Finally, an improvement to the design technique is proposed, which brings a gain of 3.3 dB in sub-channel interference power level.