Synchronization in Wireless Communications

Heidi Steendam, Mounir Ghogho, Marco Luise, Erdal Panayirci, Erchin Serpedin
2009 EURASIP Journal on Wireless Communications and Networking  
The last decade has witnessed an immense increase of wireless communications services in order to keep pace with the ever increasing demand for higher data rates combined with higher mobility. To satisfy this demand for higher data rates, the throughput over the existing transmission media had to be increased. Several techniques were proposed to boost up the data rate: multicarrier systems to combat selective fading, ultra-wideband (UWB) communications systems to share the spectrum with other
more » ... ers, MIMO transmissions to increase the capacity of wireless links, iteratively decodable codes (e.g., turbo codes and LDPC codes) to improve the quality of the link, cognitive radios, and so forth. To function properly, the receiver must synchronize with the incoming signal. The accuracy of the synchronization will determine whether the communication system is able to perform well. The receiver needs to determine at which time instants the incoming signal has to be sampled (timing synchronization). In addition, for bandpass communications, the receiver needs to adapt the frequency and phase of its local carrier oscillator with those of the received signal (carrier synchronization). However, most of the existing communication systems operate under hostile conditions: low SNR, strong fading, and (multiuser) interference, which makes the acquisition of the synchronization parameters burdensome. Therefore, synchronization is considered in general as a challenging task. The objective of this special issue (whose preparation was also carried out under the auspices of the EC Network of Excellence in Wireless Communications NEWCOM++) was to gather recent advances in the area of synchronization of wireless systems, spanning from theoretical analysis of synchronization schemes to practical implementation issues, from optimal synchronizers to low-complexity ad hoc synchronizers. In this overview of the topics that are addressed in this special issue, we first consider narrowband single-carrier systems, where narrow band means that the RF bandwidth of the system is comparable with the symbol transmission rate of the link. This is, for example, typical for a satellite link. In the paper by Lee et al. the frame synchronization problem in a DVB-S2 link was investigated. The link works at low SNR and uses forward error correction for data detection. Further, the incoming signal is disturbed by a large clock frequency offset. Under these hostile circumstances, the traditional correlation method, that looks for the synchronization sequence available in the frame header to obtain frame synchronization, gives rise to poor performance. To solve this problem, and to make the frame synchronizer more robust, the authors modify the correlation-based estimator with an additional correction term depending on the signal energy. Besides of time synchronization, phase estimation of the RF carrier used for transmission is also crucial for coherent detection. However, in mass production, to keep the cost of the devices as low as possible, cheap oscillators are used. These low-cost oscillators inherently have instabilities, causing random perturbations in the phase. The resulting phase noise causes a degradation of the system performance.
doi:10.1155/2009/568369 fatcat:52klthg37vgjxapa5iv45j366u