Co-Channel Interference in Cellular Mobile Radio Systems with Coded PSK and Diversity

In this paper, the performance of coding and diversity in narrowband wireless cellular systems affected by fading, shadowing and co-channel interference is analyzed. We consider low-order diversity, that can be practically realized for both coherent and differential phase shift keying. We assume that the shadowing random processes affecting all transmitted signals do not vary appreciably over the transmission duration. Fading, on the contrary, is assumed to vary more rapidly. Our main focus here is on outage probability. After choosing a performance indicator, its expectation is taken with respect to fading and co-channel interference, conditionally on shadowing. Hence, the resulting average performance indicator is a random variable. The probability that this random variable exceeds a specified threshold defines the outage probability. We consider as performance indicators (i) the channel cut-off rate R₀ and (ii) the bit error rate P_b of an actual coded scheme. As we are interested in interference-limited, rather than power-limited systems, we evaluate both R₀ and P_b for very high signal-to-noise ratios. Results are parameterized by the frequency reuse factor and the diversity order.     

Key payload technologies for future satellite personal communications: A European perspective

This paper deals with satellite payload architectures adequate for the provision of universal mobile telecommunication services (UMTS) by medium altitude earth and geostationary orbit (MEO and GEO) satellites. The payload concept introduced is based on a transparent transponder with onboard digital signal processing (DSP) operations and digital beamforming at the traffic carrier level (narrowband beamforming). The emphasis of the paper is on key design aspects and technology considerations of the payload processor unit (PPU), which includes multiplexing/demultiplexing and digital beamforming operations, and on the antenna and RF signal handling subsystems. For completeness, a review on the European digital technology is also presented. The development of such a payload architecture is in line with present and planned activities of the European Space Agency (ESA) for MEO and GEO orbit systems, which are also implicitly discussed in the paper.     

Impact of diversity reception on fading channels with codedmodulation. I. Coherent detection

We address the problem of designing and analyzing the performance of a coded modulation scheme for the fading channel when space diversity is used. Under fairly general conditions, a channel affected by fading can be turned into an additive white Gaussian noise (AWGN) channel by increasing the number of diversity branches. Consequently, it can be expected (and is indeed verified by our analyses and simulations) that a coded modulation scheme designed to be optimal for the AWGN channel also will perform asymptotically well on a fading channel with diversity. This paper presents bounds on the bit-error probability of a system with coded modulation and diversity for space- and time-correlated Rician flat fading. Specifically, we derive a new method which allows evaluation of the pairwise error probability extremely easily, as well as accurately and computationally fast. The accuracy achieved improves considerably on the widely used, but rather loose Chernoff bound. Starting from this analysis, we study the asymptotic behavior of the fading channel with diversity as the number of diversity branches increases, and we address the effects of diversity on coded modulation performance and design criteria, including the effect on interleaver depth (which affects the total delay of the system)     

Parallel and pipelined VLSI implementation of a staged decoder for BCM signals

This paper is devoted to VLSI implementation of a staged decoder for Block-Coded Modulation (BCM). We first review a general parallel and pipelined implementation of the decoder and we identify the parameters to be considered for optimization. A particular BCM scheme, based on the 8-PSK signal set, is chosen for a case study. Several ideas are described leading to a code-optimized design, and hardware implementation is shown. Next, we evaluate the performance of our design. In particular it is shown that, by exploiting regularity, a simple structure which achieves a throughput rate of 10 Mbps can be implemented by using 23 K transistors and 2 standard cells CMOS technology. Further optimization and simple stacking of ten processors on a single chip in a block-processing structure allows us to achieve a throughput rate of 100 Mbps with about 150 K transistors (38 K gates).     

ESA Parabolic Flights,Drop Tower and Centrifuge Opportunities for University Students

“Fly Your Thesis!—An Astronaut Experience” is an educational programme launched by the ESA Education Office that aims to offer to European students the unique opportunity to design, build, and eventually fly, a scientific experiment as part of their Master or Ph.D. thesis. Selected teams accompany their experiments onboard the Zero-G aircraft for a series of three flights, each consisting of 30 parabolas, with each parabola providing about 20 s of microgravity. ESA Education Office financially supports the flights and part of the hardware development, as well as travel and accommodation for participants. For the first edition of this programme, four student teams were selected to participate in the 51st ESA Microgravity Research Campaign in November 2009. The 2010 edition of the programme was launched in April 2009 and the final selection was announced in January 2010. In parallel, ESA Education Office is setting up two new hands-on activities to provide European university students with access to drop tower (up to 9.3 s of microgravity) and centrifuge (from 1 to 20 times Earth’s gravity) facilities. Through ELGRA, the selected student teams are working in close contact with renowned European scientists working in gravity-related research. This paper will introduce the three new educational programmes and present the selected experiments, as well as give information to students interested in the future editions.     

Impact of diversity reception on fading channels with codedmodulation. II. Differential block detection

For pt. I see ibid., vol.45, no.6, p.563-572, 1997. We study coded modulation with block differential detection in an arbitrarily correlated Rician fading channel with space diversity. Coded differential q-PSK is included in our analysis as a special case. A metric is chosen that is optimum for perfect interleaving, slow fading, and independent diversity branches. For slow fading, we compare the the cutoff rates of the channels resulting from different choices of block length N and diversity index M. Specifically, we show that block detection with diversity may or may not generate a better coding channel than usual differential detection, according to the code selected and the combination of values of M and N. In particular, for low-diversity orders (M=1,2) and for low-to-medium code rates, differential detection is still an optimal or near-optimal solution, while for high-diversity orders (M⩾2) and medium-to-high code rates (up to uncoded modulation) block detection with N>2 can provide a significant gain. An error floor always exists when fading is fast. It decreases exponentially with the product of code diversity and space diversity, so that the latter emerges as a very effective technique for lowering the error floor of a system affected by fast fading. Performance examples based on actual coding schemes are also shown     

Systolic architecture for the VLSI implementation of high-speed staged decoders/quantizers

We describe the systolic-array implementation of a block-oriented algorithm known as staged decoding, applicable to a class of signal-space codes and lattices obtained through “generalized concatenation”. By exploiting the trellis representation of block codes and the algebraic formulation of Viterbi Algorithm, we derive a very efficient symbol-level pipelined architecture of the staged processor. In order to show the range of applicability of our architecture, we consider the implementation of a staged decoder for the 8-PSK block-coded modulation (BCM) scheme with block length 8 and rate 1 bit/dimension. We obtain a decoding rate of more than 700 Mbit/s with an associated hardware complexity of less than 30 Kgates with 1μ CMOS technology. A preliminary, shorter version of this paper was presented at ICC'93, Geneva, May 1993.     

A multiuser approach to narrowband cellular communications

We compare three receivers for coded narrowband transmission affected by fading and co-channel interference. The baseline receiver is based on conventional diversity reception with maximal-ratio combining. A multiuser approach allows us to derive a maximum-likelihood multiuser receiver and its reduced-complexity suboptimal version. Finally, a decorrelating diversity receiver, which seeks a tradeoff between performance and complexity, is studied. Closed-form performance parameters are derived for all the proposed receivers in the case of coded coherent PSK and independent frequency nonselective Rayleigh fading     

Impact of diversity reception on fading channels with codedmodulation. III. Co-channel interference

For pt.II see ibid., vol.45, no.6, p.55-67, 1997. In previous work, we have studied the impact of diversity on coded digital communication systems operating over fading channels. In particular, we have shown that diversity may be thought of as a way of making the channel more similar to a Gaussian one. The present paper extends this analysis to fading channels affected by co-channel interference (CCI). Three receiver models are examined, namely, with coherent detection and perfect channel-state information (CSI), with differential; and with pilot-tone detection. We study the effect of diversity on the irreducible error floor caused by CCI and fading, and the asymptotic behavior of the channel as the diversity order increases. Our results show that, when perfect CSI is available, diversity is able to turn asymptotically the channel into a CCI-free additive white Gaussian noise (AWGN) channel with the same signal-to-noise ratio (SNR). On the other hand, differential and pilot-tone detection do not remove interference in the limit. Nevertheless, also with these detection schemes, diversity achieves significant gains when the SNR is large enough. Calculation of the channel cutoff rate provides guidelines for the design of coded systems with CCI in fading environments. A wide range of examples, validated by computer simulation, illustrates our conclusions