Impact of Shadowing Correlation on Coverage of Multihop Cellular Systems

The impact of spatial correlation of shadowing on the coverage of TDMA multihop cellular systems is investigated in single-cell environments. The introduction of relaying capabilities to cellular systems may enhance the cell coverage as follows. Changing single-hop transmission to multihop transmission reduces per-hop path loss. In addition, since a multihop route is selected among a number of alternatives, the use of mobile stations suffering from severe shadowing can be decreased. In most studies on multihop cellular systems, shadowing is modeled as a location-independent log-normal random variable; however, adjacent shadowing values are spatially correlated because shadowing is caused by terrain configuration or obstacles between the transmitter and receiver. Thus, coverage enhancement due to relaying capabilities may not be achieved as expected. In this paper, first, according to the commonality between multihop transmission and symbol rate control, a similar methodology to formulate the spectral efficiency (SE) and outage probability of rate-adaptive cellular systems is used to estimate these performances of multihop cellular systems. Second, we investigate the impact of decorrelation distance, whose typical value for the urban environment is 20 meters, on the coverage of multihop cellular systems. By using a model for spatially correlated shadowing, numerical results reveal that when the coverage of single-hop cellular systems is ten times larger than the decorrelation distance, the introduction of relaying capability may enhance the coverage without significant degradation due to the spatial correlation of shadowing.