Dr Weisi Guo said: "One of the key concerns with 4G roll out is that the promise of greater speed cannot be realized in areas of poor coverage. Poor coverage typically occurs in indoor areas in cities. This is where most of the mobile data transfer occurs, so it is a key area to consider.

"While some operators have promised that indoor coverage will be improved to a staggering 98%, we have strong reservations about this. Whilst the low frequency (800MHz) spectrum does indeed improve signal propagation characteristics, many urban indoor areas are not propagation-limited.

"In cities, most of the coverage is interference-limited due to the high cell density. In this scenario, the transmit frequency has no impact on the performance of the network, and therefore, we expect the coverage of 4G to be the same as 3G in indoor areas. This renders the benefits of 4G to mostly outdoor areas with good coverage."