arXiv subjects

Georg Böcherer

Publications and source records attributed to Georg Böcherer.

57 records · Page 4Linked to original sources

arXiv2009

Cooperative Protocols for Random Access Networks

Cooperative communications have emerged as a significant concept to improve reliability and throughput in wireless systems. On the other hand, WLANs based on random access mechanism have become popular due to ease of deployment and low cost. Since cooperation introduces extra transmissions among the cooperating nodes and therefore increases the number of packet collisions, it is not clear whether there is any benefit from using physical layer cooperation under random access. In this paper, we develop new low complexity cooperative protocols for random access that outperform the conventional non cooperative scheme for a large range of signal-to-noise ratios.

cs.IT↗

arXiv2008

Maximum Entropy Rate of Markov Sources for Systems With Non-regular Constraints

Using the concept of discrete noiseless channels, it was shown by Shannon in A Mathematical Theory of Communication that the ultimate performance of an encoder for a constrained system is limited by the combinatorial capacity of the system if the constraints define a regular language. In the present work, it is shown that this is not an inherent property of regularity but holds in general. To show this, constrained systems are described by generating functions and random walks on trees.

cs.IT↗

arXiv2008

Theoretical Analysis of the Energy Capture in Strictly Bandlimited Ultra-Wideband Channels

The frequency selectivity of wireless communication channels can be characterized by the delay spread Ds of the channel impulse response. If the delay spread is small compared to the bandwidth W of the input signal, that is, Ds*W approximately equal to 1, the channel appears to be flat fading. For Ds*W >> 1, the channel appears to be frequency selective, which is usually the case for wideband signals. In the first case, small scale synchronization with a precision much higher than the sampling time T = 1/W is crucial. In this paper, it is shown by analytical means that this is different in the wideband regime. Here synchronization with a precision of T is sufficient and small scale synchronization cannot further increase the captured energy at the receiver. Simulation results show that this effect already occurs for W > 50MHz for the IEEE 802.15.4a channel model.

cs.IT↗