DSP-Based Carrier Acquisition and Tracking for Burst TDMA Mobile Land and Satellite Receivers

The theory of optimum receiver data wireless detection requires synchronization signal parameters that are accurately aligned with those in the transmitter. Therefore, synchronization should be the most robust and reliable element in the receiver design process, ensuring that data detection can continue over deteriorating channels, such as those with fading and large carrier offsets. Furthermore, the available processing time at the receiver for burst-type systems is very short, and computationally efficient techniques are required in order to acquire and track the received signal quickly. Computationally efficient synchronization methods also benefit receiver power consumption. Carrier frequency offsets can be large due to Doppler shifts or frequency uncertainties in the receiver and transmitter frequency mixing stages [2, 4]. This problem may sometimes be circumvented by imposing stringent requirements on the frequency stability of the transmit and receive oscillators. For example, a receiver with a frequency offset tolerance of 100 hertz, inclusive of Doppler shifts, requires the use of an oscillator with stability better than 0.10 parts per million (PPM). This is a severe constraint given that such an oscillator has to be a temperature-compensated crystal oscillator and (TXCO), which requires large amounts of DCpower and a long warm-up time and is both bulky in size and expensive. Therefore, we must seek alternate methods for frequency compensation that use less accurate frequency sources. Since the cost-efficient implementation of time division multiple access (TDMA) terminals generally requires extensive use of digital signal processing techniques, it may be more convenient to implement frequency offset estimation and correction algorithms that relieve the stringent requirements on the master frequency oscillator in the receiver [7]. Furthermore, it is desired that such algorithms be limited to the digital signal processing part of the radio. This means that conventional techniques, such as analog voltage control oscillator steering, are not favored. This article describes modeling, analysis and simulation results of an all-digital carrier synchronization algorithm for burst type TDMA signals subjected to additive white Gaussian noise (AWGN) and severe Doppler frequency shift that is relatively large compared to the data rate of the receiver. The algorithm detailed in the coming sections is well suited for an all digital receiver implemented using either digital signal processing (DSP) or ASIC techniques. Although the detailed algorithm is shown here only for BPSK and QPSK TDMA satellite burst receivers, it could easily be extended for applications in other current wireless systems, such as GSM, IS-136, personal handy-phone system (PHS), multimedia cable or local multipoint distribution (LMDS).