A space communications study Final report, 15 Sep. 1966 - 15 Sep. 1967

Investigation of signal to noise ratios and signal transmission efficiency for space communication system

Performance Analysis of a Dual-Hop Cooperative Relay Network with Co-Channel Interference

This paper analyzes the performance of a dual-hop amplify-and-forward (AF) cooperative relay network in the presence of direct link between the source and destination and multiple co-channel interferences (CCIs) at the relay. Specifically, we derive the new analytical expressions for the moment generating function (MGF) of the output signal-to-interference-plus-noise ratio (SINR) and the average symbol error rate (ASER) of the relay network. Computer simulations are given to confirm the validity of the analytical results and show the effects of direct link and interference on the considered AF relay network

Comparison of direct and heterodyne detection optical intersatellite communication links

The performance of direct and heterodyne detection optical intersatellite communication links are evaluated and compared. It is shown that the performance of optical links is very sensitive to the pointing and tracking errors at the transmitter and receiver. In the presence of random pointing and tracking errors, optimal antenna gains exist that will minimize the required transmitter power. In addition to limiting the antenna gains, random pointing and tracking errors also impose a power penalty in the link budget. This power penalty is between 1.6 to 3 dB for a direct detection QPPM link, and 3 to 5 dB for a heterodyne QFSK system. For the heterodyne systems, the carrier phase noise presents another major factor of performance degradation that must be considered. In contrast, the loss due to synchronization error is small. The link budgets for direct and heterodyne detection systems are evaluated. It is shown that, for systems with large pointing and tracking errors, the link budget is dominated by the spatial tracking error, and the direct detection system shows a superior performance because it is less sensitive to the spatial tracking error. On the other hand, for systems with small pointing and tracking jitters, the antenna gains are in general limited by the launch cost, and suboptimal antenna gains are often used in practice. In which case, the heterodyne system has a slightly higher power margin because of higher receiver sensitivity

Performance evaluation for communication systems with receive diversity and interference

Optimum combining (OC) is a well-known coherent detection technique used to combat fading and suppress cochannel interference. In this dissertation, expressions are developed to evaluate the error probability of OC for systems with multiple interferers and multiple receiving branches. Three approaches are taken to derive the expressions. The first one starts from the decision metrics of OC. It facilitates obtaining closed-form expressions for binary phase-shift keying modulation. The second approach utilizes the moment generating function of the output signal to interference plus noise ratio (SINR) and results in expressions for symbol and bit error probability for multiple phaseshift keying modulation. The third method uses the probability density function of the output SINR and arrives at expressions of symbol error probability for systems where the interferers may have unequal power levels. Throughout the derivation, it is assumed that the channels are independent Rayleigh fading channels. With these expressions, evaluating the error probability of OC is fast, easy and accurate. Two noncoherent detection schemes based on the multiple symbol differential detection (MSDD) technique are also developed for systems with multiple interferers and multiple receiving branches. The first MSDD scheme is developed for systems where the channel gain of the desired signal is unknown to the receiver, but the covariance matrix of the interference plus noise is known. The maximum-likelihood decision statistic is derived for the detector. The performance of MSDD is demonstrated by analysis and simulation. A sub-optimum decision feedback algorithm is presented to reduce the computation complexity of the MSDD decision statistic. This suboptimum algorithm achieves performance that is very close to that of the optimum algorithm. It can be shown that with an increasing observation interval, the performance of this kind of MSDD approaches that of OC with differential encoding. The second MSDD scheme is developed for the case in which the only required channel information is the channel gain of the interference. It is shown that when the interference power level is high, this MSDD technique can achieve good performance

Recursive Detection of M-Ary Signals over Fast Varying Mobile Communication Channel

          Mobile radio is characterized by a fast time varying channel. Conventional detectors which designed optimal for non-fading channel exhibit a limited performance in fast time varying channel. In this paper a recursive detector for M-ary signals over fast time varying mobile communication channel is introduced. The proposed detector continuously estimates the channel directly within the metric calculation of the log-likelihood function in a recursive manner. The estimation of the channel is performed by the covariance form of the recursive least square approach. The performance of the detector is evaluated in terms of the misdetection probability. The effects of timing and phase offsets on the performance of detector are examined by simulation. Simulation results show that the proposed detector can accommodate the fast time varying channel with adequate performance

A combined PSK/ASK transmission system for commercial telephony via satellite

This study addresses three modulation schemes capable of increasing the voice channel capacity of the INTELSAT TDMA/DSI System operating with INTELSAT V spacecraft. In particular, a combination digital Amplitude-Shift Keying/Phase-Shifting Keying (APK) technique is evaluated with respect to signal design, thermal noise performance, bandwidths limitations, co-channel interference, adjacent channel interference, TWT distortion and modem complexity in an INTELSAT TDMA system environment. In a linear channel some APK signal designs are known to require significantly less average SNR than PSK to achieve the same probability of symbol error. However, when operated through a satellite channel containing at least one TWT, the reduction in average power required to accommodate amplitude variations causes APK performance to fall below that of PSK for the same alphabet size. Signal predistortion and/or TWT linearization can eliminate the effect of TWT distortion and restore the performance advantage, although the overall performance of APK is still inferior to PSK. However, in a heavily interference limited environment, such as INTELSAT V, the lower average power requirements caused an APK system to perform better, in some cases considerably better, than the corresponding PSK case. Modem implementation considerations include how the signal set can be generated, the type and method of predistortion compensation, the detection method and the equipment required for the reconstruction of phase and amplitude references. The evaluation techniques of APK described include mathematical models, computer simulations (including the development of a unified error performance expression) and logical extrapolation from the QPSK case. Finally, a simple 8 level APK hardware modem was constructed and evaluated. It is concluded that an APK system may be of advantage as a retrofit in the INTELSAT TDMA system operating at 6/4 GHz, but be of significant advantage at 14/11 Ghz where the higher signal/noise ratios can yield an increase in capacity of up to 50 percent