John Lodge

Space-time coding in mobile Satellite communications using dual-polarized channels

The use of dual-orthogonal polarization (horizontal/vertical or circular right-hand/left-hand polarizations) can increase the rate of transmission of satellite communication systems by a factor of two. However, the cross polar discriminations (XPDs) of the satellite and earth station antennas may be large enough to severely interfere between the two polarizations. In this paper, we investigate the use of space-time coding techniques in satellite-land mobile systems using dual-polarized transmit and receive antennas. In particular, we show that we can achieve significant gains by using layered space-time coding concepts and iterative detection and decoding receivers in communications systems employing polarization diversity channels in the presence of line-of-sight components.

A comparison of data modulation techniques for land mobile satellite channels

Several modulation schemes for transmitting data over land mobile satellite channels are compared using a Monte Carlo simulation. Schemes under consideration include differentially detected minimum shift keying (DMSK), differentially detected filtered offset quadrature phase shift keying (DOQPSK), and coherently detected binary phase shift keying with transparent tone-in-band processing (BPSK-TTIB). The transmission of data to and from a mobile radio, which is also capable of operating as an amplitude companded single sideband radio, is the application considered here. The nominal bit rate is 2400 bit/s, while the nominal channel spacing is 5 kHz. DOQPSK with nonredundant single-error correction (SEC) is shown to be a promising candidate. It is capable of outperforming DMSK with SEC by more than 1 dB. Techniques that send a reference signal along with a PSK signal and then perform coherent detection, such as BPSK-TTIB, are also shown to be inferior to DOQPSK with SEC for the class of channels considered here.

A high capacity third‐generation mobile satellite system design

This paper describes a CDM/CDMA based approach for a 3-rd generation multi-beam satellite mobile and personal communications system using Highly Elliptical Orbit (HEO) satellites. The forward link uses a synchronous CDM intra-beam/asynchronous CDM inter-beam approach, while the return link uses a quasi-synchronous CDMA intra-beam/asynchronous CDMA inter-beam approach. Using probabilistic analysis, these approaches are shown to provide higher forward and return link capacities than equivalently synchronized FDM/FDMA approaches. Forward link transmissions are modulated using QPSK. Return link transmissions are modulated using either ϕ/4-QPSK or precompensated frequency modulation (PFM4). PFM4 is intended for use with a saturated amplifier in low-cost/power-efficient, e.g. hand-held, terminals, and can be demodulated using a ϕ/4-QPSK receiver. All forward and return link transmissions are coded using a rate 1/2, constraint length 9, convolutional code. The paper summarizes several key tradeoffs and the resulting system design.

Approaching near-capacity on a multi-antenna channel using successive decoding and interference cancellation receivers

In this paper, we address the problem of designing multirate codes for a multiple-input and multiple-output (MIMO) system by restricting the receiver to be a successive decoding and interference cancellation type, when each of the antennas is encoded independently. Furthermore, it is assumed that the receiver knows the instantaneous fading channel states but the transmitter does not have access to them. It is well known that, in theory, minimum-mean-square error (MMSE) based successive decoding of multiple access (in multi-user communications) and MIMO channels achieves the total channel capacity. However, for this scheme to perform optimally, the optimal rates of each antenna (per-antenna rates) must be known at the transmitter. We show that the optimal per-antenna rates at the transmitter can be estimated using only the statistical characteristics of the MIMO channel in time-varying Rayleigh MIMO channel environments. Based on the results, multirate codes are designed using punctured turbo codes for a horizontal coded MIMO system. Simulation results show performances within about one to two dBs of MIMO channel capacity.

Separable concatenated convolutional codes: The structure and properties of a class of codes for iterative decoding

In this paper a brief overview of the concept of iterative processing is provided. Then a code construction for convolutional codes, that results in a signal structure amenable to iterative processing, is studied. This construction is analogous to product coding for block codes. It is shown that the construction shares a number of properties with the product coding construction, including the property that it is commutative. The relationship between the free distance and the interleaving factors is examined, and then exemplified with computer simulation results.

Approaching near-capacity on a multi-antenna channel using multirate encoding and successive decoding receivers

We address the problem of designing multirate codes for a multiple-input and multiple-output (MIMO) system by restricting the receiver to be a successive decoding and interference cancellation type, when each of the input signals is encoded independently. It is assumed that the receiver knows the instantaneous fading channel states but the transmitter does not have access to them. We design a multirate coded MIMO system using punctured turbo codes and demonstrate the efficiency of the proposed scheme using simulation results. In particular, the simulation results show performance within 2 dB of MIMO channel capacity.

An Alternative Approach to the Design of Interleavers for Block Turbo Codes

In this paper we describe two methods of interleaving for use with generalized product block codes that can be decoded using a “turbo” decoding strategy. These methods are designed to avoid certain specific error patterns. One method has a number theoretic basis while the other uses finite projective planes. Simulation results are presented.

Adaptive coding and modulation for return satellite links using binary turbo coding

A turbo code that is based on an 8-state binary constituent code is considered in this paper for use in an adaptive coding and modulation system for a return satellite link. The paper presents the results of finding good puncture-constrained dithered relative prime interleavers along with data puncture patterns to provide the required performance. A tradeoff between waterfall and flare performance can be made by selecting the best puncture masks for the required error rate. The performance of the turbo code with a packet size of 1504 data bits is presented for the following modulations: BPSK, QPSK, 8 PSK and 16 APSK. A comparison with other coding strategies shows that this code is an attractive option for use in a return satellite link application using adaptive coding and modulation.

Separable concatenated codes with iterative map filtering

In practice, very efficient signalling over radio channels requires more than designing very powerful codes. It requires designing very powerful codes that have special structure so that practical decoding schemes can be used with excellent, but not necessarily optimal, results. Examples of two such approaches include the concatenation of convolutional and Reed-Solomon coding, and the use of very large constraint-length convolutional codes with reduced-state decoding. In this paper, powerful codes are obtained by using simple block codes to construct multidimensional product codes. The decoding of multidimensional product codes, using separable symbol-by-symbol maximum a posteriori (MAP) “filters”, is described. Simulation results are presented for three-dimensional product codes constructed with the (16,11) extended Hamming code. The extension of the concept to concatenated convolutional codes is given. The relationship between the free distance and the interleaving factors is examined, and then exemplified with computer simulation. Potential applications are briefly discussed.

Forward error correction for an enhanced SARSAT distress message

This paper presents a proposed enhancement to the current SARSAT distress message that is backward-compatible with the existing local user terminals (LUT) (i.e., ground stations) receivers. Additional coding is appended to the current message to allow for better performance for the new LUTs, soft-decision decoding is used in the evaluation of the current and enhanced format. Performance results on the AWGN channel are presented. It is shown that near maximum-likelihood performance is achieved for the new code format.