A new contention-based multi-access protocol, named status sense multiple access (S/sup 2/MA), is introduced. S/sup 2/MA is synchronous TDMA in its framing but it possesses many features of random access. The approach of S/sup 2/MA is geared towards integrating heterogeneous classes of customers over a common broadcast channel. The performance of this protocol with two classes of customers, such as voice and data, is analyzed. Unlike fixed and some moveable-boundary approaches of integrating voice and data, here no slot is wasted, except for possible collision, as long as there is a demand for the slot from either of the two classes. Therefore, the channel utilization efficiency can be very high.>

A generalized quadrature-quadrature phase shift keying (Q/sup 2/PSK) signaling format is considered for differential encoding and differential detection. Performance in the presence of additive white Gaussian noise (AWGN) is analyzed. Symbol error rate is found to be approximately twice the symbol error rate in a quaternary DPSK system operating at the same E/sub b//N/sub 0/. However, the bandwidth efficiency of differential Q/sup 2/PSK is substantially higher than that of quaternary DPSK. In differential detection, it is quite reasonable to suspect that errors tend to occur in pairs. It is shown that when the error is due to AWGN, the ratio of double error rate to single error rate can be very high, and the ratio may approach zero at high signal-to-noise ratio. In an attempt to improve the error rate performance, differential detection through maximum-likelihood decoding based on multiple or N symbol observations is considered.>

Channel coding due to trellis modulation has been proved to be useful for bandlimited channels. However, these modulations, mostly designed with n-use of 2D signals, are primarily aimed at coding gain only. It is pointed out that utilization of all available signal dimensions, which is limited by the time-bandwidth product, may improve the bandwidth efficiency and simultaneously bring an additional coding gain. Trellis coding with a spectrally efficient 4D signal set based on Q/sup 2/PSK is addressed. Without any expansion of the Q/sup 2/PSK signal set, a simple hand-designed 16-state trellis code provides a coding gain of 6.02 dB. With the same number of states in G. Ungergoeck's (1982) 8-PSK trellis, the gain is 4.1 dB. In low intersymbol interference situations, the bandwidth efficiency of this coded Q/sup 2/PSK is twice that of coded 8-PSK; if both operate at 2 b/s Hz and P/sub b/(E)=10/sup -5/, the coded Q/sup 2/PSK provides a saving of about 4 dB over the coded 8-PSK. Some fully connected trellises with an expanded signal due to 2-use of Q/sup 2/PSK signals are also presented. Two such codes ar rate-7/8 achieve a gain of 5.45 dB with only eight states.>

Quadrature-quadrature phase-shift keying (Q/sup 2/PSK) is a spectrally efficient modulation scheme which utilizes available signal space dimensions in a more efficient way than two-dimensional schemes such as QPSK and MSK (minimum-shift keying). It uses two date shaping pulses and two carriers, which are pairwise quadrature in phase, to create a four-dimensional signal space and increases the transmission rate by a factor of two over QPSK and MSK. However, the bit error rate performance depends on the choice of pulse pair. With simple sinusoidal and cosinusoidal data pulses, the E/sub b//N/sub 0/ requirement for P/sub b/(E)=10/sup -5/ is approximately 1.6 dB higher than that of MSK. Without additional constraints, Q/sup 2/PSK does not maintain a constant envelope, however, a simple block coding can provide a constant envelope. This coded signal substantially outperforms MSK and TFM (time-frequency multiplexing) in bandwidth efficiency. Like MSK, Q/sup 2/PSK also has self-clocking and self-synchronizing ability. An optimum class of pulse shapes for use in Q/sup 2/PSK format is presented. One suboptimum realization achieves the Nyquist rate of 2 b/s/Hz using binary detection.>