Transmitter Precoding for ICI Reduction in Closed-Loop MIMO OFDM Systems

The mitigation of intercarrier interference (ICI) in closed-loop single-input-single-output (SISO) and multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) is considered. The authors show that the ICI coefficient matrix is approximately unitary and exploit this property to design a nonlinear Tomlinson-Harashima precoder for the reduction of ICI in closed-loop SISO OFDM and orthogonal space-time block-coded (OSTBC) MIMO OFDM. With the proposed design, the transmitter does not need to know the frequency offsets, and hence, their impact on the bit error rate (BER) is significantly reduced. Moreover, for spatially correlated MIMO channels, the precoder and OSTBC OFDM perform with a negligible BER-performance loss     

Phosphite additives and their transformation products in polyethylene packaging for G-irradiation

Infrared (IR) spectroscopy has been used to identify and quantify the phosphite antioxidant, tris(2,4-di-tert.butylphenyl) phosphite, and its corresponding phosphate in high density polyethylene (HDPE) food trays, both in the original, commercial trays and also as a function of gamma-irradiation and post-irradiation, storage conditions. This direct method of inhibitor analysis complements time-consuming (some times non-quantitative) extraction methods, which for organo-phosphites are complicated by their facile conversion to phosphates by peroxidic impurities in the solvent. Because of the complete destruction of phosphite to give mainly phosphate at quite low gamma-irradiation doses (approximately 5 kGy) and phosphate formation during melt processing and radiation sterilization of these HDPE trays must take into account products from the irradiation of phosphate. Any residual phosphite is lost progressively in post-irradiation reactions, which are complex, producing a less than-quantitative yield of phosphate.     

Spectral analysis of waiting time jitter in the presence of stuff threshold modulation

The Fourier transform of waiting time jitter in the presence of stuff threshold modulation is derived. Comparisons are made between power spectral densities and RMS jitter obtained analytically and by simulation. The Fourier transform enables the jitter performance to be evaluated in the presence of alternative stuff threshold modulation waveforms, required for example, in some SONET applications.<>     

Transmission performance analysis of a new class of line codes for optical fiber systems

A family of mB(m+1)B binary, nonalphabetic, balanced line codes is presented that is suitable for high bit rate (>or=135 Mb/s) optical fiber transmission due to its relatively simple encoding and decoding rules. Here, B represents a block of m bits, where m is an odd number. The coding, decoding, and bit error rate (BER) performance of the codes are discussed. Statistical and spectral analysis for the specific case in which the number of bits, m, equals seven, is presented. This makes possible a detailed comparison of the proposed code with conventional 7B8B codes.<>     

A novel CDMA multiuser interference cancellation receiver withreference symbol aided estimation of channel parameters

A novel multistage successive interference cancellation scheme is proposed which operates on the reverse code-division multiple-access (CDMA) link using binary phase shift keying (BPSK) modulation, coherent detection and reference symbols to obtain channel estimates. The results of a single cell multiuser investigation demonstrate increased traffic capacity. However, this increase is initially very moderate due to corruption of the channel estimates by interference from symbols not yet demodulated and cancelled. A modification in the transmitted signal structure addressing this problem is proposed. The results of a single cell analysis of the modified cancellation scheme demonstrate that the system's traffic capacity reaches approximately 80% of that of a multistage successive interference cancelling receiver operating with the perfect knowledge of channel parameters. A subsequent multicell investigation shows that for a hexagonal cell geometry with a path loss exponent of four and without any forward error correction (FEC) coding or cell sectorization, the system capacity compares very favorably with that of the IS-95 system, which employs powerful error control coding. Capacities with other path loss exponents and cell geometries are also investigated. The results show a substantial traffic capacity increase over that of a comparable receiver without interference cancellation     

An analysis of the effect of chip timing jitter in MC-CDMA systems

We investigate the effect of chip synchronization error (or chip timing jitter) in a multicarrier-code division multiple access (MC-CDMA) scheme. The chip timing jitter is modeled by a stationary random process with a known statistic, and the error produced by the jitter is reduced to an additive source of noise. This decomposition is useful because it allows for the use of analytical methods for the computation of the error probability. First, the analysis has been applied to the simple Gaussian channel; afterwards, it has been extended to a multipath fading channel typical of large indoor areas. Use of a semi-analytical approach has been the key factor in obtaining reliable results at moderate computational complexity     

Reference Symbol Assisted Multi-Stage Successive Interference Cancellation for CDMA Wireless Communication: Robustness to Parameter Imperfections with Biphase and Quadriphase spreading

This paper investigates the sensitivity to system imperfections of a reference symbol assisted multi-stage successive interference cancelling (RAMSIC) receiver. Reverse link of a CDMA system with binary antipodal modulation and coherent detection is considered. Performance of systems using either biphase and quadriphase spreading is compared under different operating conditions. Analysis of a conventional matched filter receiver operating on an AWGN channel reveals that when the number of users is small (such that the multiple access interference cannot be accurately modelled as Gaussian), quadriphase spreading has a significant advantage over biphase spreading. This advantage, however, disappears when the number of users per sector is large (of the order necessary for the multiple access interference to be considered Gaussian). Results for the RAMSIC receiver with quadriphase spreading, on the other hand, show that for hexagonal cell geometry with path loss exponent of 4 and without any forward error correction coding, the traffic capacity is between 1.17 and 1.67 times that of the IS-95. These numbers represent a significant increase over those obtained with biphase spreading. Further investigation with nonidealized cell geometries and other path loss exponents also shows substantial capacity improvement over that of conventional correlator receivers. Performance losses due to nonideal transmitter power amplifier gating, imperfect power control and synchronization errors in the RAKE receiver are also determined. The results for biphase spreading show that for path loss exponent of 4, imperfect amplifier gating causes relatively minor decrease in the traffic capacity, while no such effect is observed for path loss exponents of 2 and 3. As expected, relaxing of power control for both biphase and quadriphase spreading has a similar capacity reducing effect. In spite of these two effects the resultant capacity is still significantly higher than that with the conventional matched filter receiver. Capacity increase with quadriphase over biphase spreading is between 1.4 and 2.0 times. Chip synchronization errors of the order to be expected in a properly designed conventional CDMA system have only minimal effect on performance. Therefore, we conclude that conventional synchronization algorithms should perform adequately with successive interference cancelling receivers considered in the paper.     

Performance of spatially multiplexed MC-CDM with zero-forcing unified successive interference cancellation detection

Spatially multiplexed multicarrier code-division multiplexing (SM-MC-CDM) is a multiple-input multiple-output, orthogonal frequency division multiplexing (MIMO-OFDM) communication technique with multiple antennas used for spatial multiplexing and with frequency domain spreading on each antenna. Unified successive interference canceller (U-SIC) is an efficient detector recently introduced for SM-MC-CDM. This paper presents an analytical approach to the performance of zero-forcing (ZF) U-SIC for SM-MC-CDM communications. For a system with an equal number of transmit and receive antennas, an approximation for the probability density function of post-detection signal-to-noise ratio (SNR) is used to derive a closed-form analytical upper bound and approximations for the probability of error and ergodic capacity. It is shown that SM-MC-CDM with ZF U-SIC is able to achieve higher diversity order than that achieved by ZF and minimum mean squared error (MMSE) V-BLAST detectors used on each subcarrier of a MIMO-OFDM system with the same number of subcarriers. The diversity order obtained increases with the number of subcarriers. It is also shown that the ergodic capacity of the system decreases with increasing number of subcarriers.     

Strategies for management of connection oriented data sessionsemploying the idle times in cellular telephony

We consider strategies for and performance of a class of connection-oriented data session services that might be supported using only the idle times between telephone calls on the channels of a cellular radio system. Two types of service are envisaged: a short transaction service and a suspendable data session service. We give expressions for the mean active and inactive times for data sessions and show how session assignment and displacement strategies can shape the distributions of session active and inactive times. We find useful amounts of capacity in the background of telephony systems even at high load, but in its raw form the opportunities for data transmission, and the data session suspension times implied, are rather large-grained for interactive data sessions. However, enforced time-sharing can improve these statistics for interactive data uses. With prioritized session assignment, a number of logical data sessions can be supported providing a range of service characteristics onto which interactive users, mobile fax, paging, navigation, and fleet tracking applications can be mapped in decreasing order of required session availability