Abstracts of Forthcoming Manuscripts Space-Time Codes for High Data Rate Wireless Communication: Performance Criteria in the Presence of Channel Estimation Errors, Mobility and Multiple Paths

Field: Computer Science (Physical Sciences)

Space-time coding is a bandwidth and power efficient method of communication over fading channels that realizes the benefits of multiple transmit antennas. Specific codes have been constructed using design criteria derived for quasi-static flat Rayleigh or Rician fading, where channel state information is available at the receiver. It is evident that the practicality of space-time codes will be greatly enhanced if the derived design criteria remain valid in the absence of perfect channel state information. It is even more desirable that the design criteria not be unduly sensitive to frequency selectivity and to the Doppler spread. This paper presents a theoretical study of these issues beginning with the effect of channel estimation error. Here it is assumed that a channel estimator extracts fade coefficients at the receiver and for constellations with constant energy, it is proved that in the absence of ideal channel state information the design criteria for space-time codes is still valid. The analysis also demonstrates that standard channel estimation techniques can be used in conjunction with space-time codes provided that the number of transmit antennas is small. We also derive the maximum-likelihood detection metric in the presence of channel estimation errors. Next, the effect of multiple paths on the performance of space-time codes is studied for a slowly changing Rayleigh channel. It is proved that the presence of multiple paths does not decrease the diversity order guaranteed by the design criteria used to construct the space-time codes. Similar results hold for rapid fading channels with or without multiple paths. The conclusion is that the diversity of order promised by space-time coding is achieved under a variety of mobility conditions and environmental effects. Abstract— Passive optical matched-filtered detection (MFD) has been employed in many proposed optical pulse code-division multiple-access (CDMA) system implementations, driving the development of unipolar pseudo-orthogonal codes (incoherent). In this paper, coherent opticalpulse CDMA systems based on coherent correlation detection (CCD), throough homodyne correlation detection (HCD) and self-HCD directly in the optical domain is proposed. With HCD, optical sequences from a pulsed laser, modulated by the data and encoded by an optical delay-line encoder, are multiplexed in an optical fiber network. At the receiver, the optical code sequence of the intended user is locally generated. Through proper code and carrier phase synchronization, the local optical code is multiplied with the received signal chip by chip via an optical correlator Publisher Item Identifier S 0090-6778(99)00806-5. consisting of a 3-dB coupler and a balanced detector. Thresholding is performed in the electrical domain after integration of the optical correlator output over one bit interval. The self-HCD approach utilizes two bipolar code sequences multiplexed alternately in time, obviating the need for the generation of a local code at the receiver. The received signal is divided at the receiver, decoded by two encoders (matched to those at the transmitters) and correlated via the optical correlator. The removal for the need of the local oscillator avoids the stringent implementation issues with HCD such as optical frequency stability and carrier phase noise. Following a description of the two implementations, system performances are theoretically analyzed and a comparison of the several approaches given. Abstract— The Synchronous Residual Time Stamp (SRTS) is one approach approved for the encoding and transporting of the continuous bit rate (CBR). Service clock in AAL1 (ATM Adaptation Layer 1) allowing CBR services to be transported in ATM cells over the B- ISDN. It has been shown by the authors and others that the SRTS Method generates waiting time jitter analogous to that produced by other synchronization processes such as pulse stuffing synchronization. Modeling of the synchronization process as it applies to the SRTS method requires a time-domain aproach to produce an exact expression of the jitter. In this paper, we apply a new time domain analysis technique previously developed by the authors to derive the expressions for the jitter specgtrum of the synchronization process in the presence of input jitter on the service clock. Futhermore, the particular form taken by the jitter spectrum when the input jitter is sinusoidal is also found. Experiments verifying the synchronization process jitter spectrum, both with and without sinusoidal input jitter are reported. Confirmation is also provided that it is possible to approximate timing jitter by phase jitter as long as certain frequency-amplitude limits are observed.