VoLTE (Voice over LTE) is expected to be deployed in the near future to provide voice services in LTE networks. There is also an increasing need for much higher data capacity as a result of smartphone proliferation. Therefore, it is important to investigate and optimize the LTE networks in the presence of voice and data traffic. In this paper, we evaluate the performance of LTE Downlink when both VoLTE and data users are present. Both Macro only (homogenous) and HetNet (heterogeneous with Macro and small cells) scenarios are considered. It is shown that HetNet with Pico cell range expansion significantly improves both the system data performance and VoLTE capacity.

In resource limited, large scale sensor networks, cooperative communication over multiple hops offers opportunities to save power: intermediate nodes between source and destination act as cooperative relays. In order to exploit spatial diversity, protocols coupled with space-time coding strategies are proposed herein and analyzed for distributed cooperative communication. In contrast to prior work, multi-hop (versus two-hop) schemes are developed and analyzed for amplify-and forward type of communication protocols. First, the Alamouti based two-hop scheme proposed by Hua et al and analyzed by Jing & Hassibi is generalized to an arbitrary number of hops L, and a general approximation for the pairwise error probability (PEP) at high SNR is obtained. This expression is used to provide a close approximation to the achievable diversity gain of the scheme. It is further shown that the diversity decreases with L, for large, but finite signal-to-noise ratio (SNR). This motivates the subsequent development of new distributed multihop protocols to mitigate the diversity losses and, hence, yield improved performance. This work presents two such strategies as well as their diversity characterization, which are analyzed for the specific case of L = 3 hops and shown to exhibit improved performance at high SNR. These schemes are based on the structure of the rate-half codes proposed by Tarokh and the square-matrix embeddable codes of Tirkkonen & Hottinen.

Space-time block codes (STBCs) have attracted recent interest due to their ability to take advantage of both space and time diversity to reliably transmit data over a wireless fading channel. In many cases, their design is based on asymptotically tight performance criteria, such as the worst-case pairwise error probability (PEP) or the union bound. However, these quantities fail to give an accurate performance picture, especially at low signal-to-noise ratio, because the classical union bound is known to be loose in this case. This paper develops tighter performance criteria for STBCs which yield considerably better bounds. First, the union bound is developed as the average of the exact PEPs. By noting that some of the terms in the bound are redundant, a second bound is obtained by expurgation. Since this still yields a loose bound, a tighter bound, denoted as the progressive union bound (PUB), is obtained. Because the PUB cannot be computed in closed form, in its most general case, and to avoid computing a high-dimensional numerical integration, its saddlepoint approximation is developed. In addition to the significant improvement of the PUB analysis over other bounding methods, it is also shown that codes designed to optimize the PUB can perform better than those obtained by the looser criteria

In resource limited, large scale underwater sensor networks, cooperative communication over multiple hops offers opportunities to save power when intermediate nodes between source and destination act as cooperative relays. Herein, protocols coupled with space-time block code (STBC) strategies are analyzed for distributed cooperative communication in underwater channels. Amplify-and-forward type protocols are considered, in which the relays do not attempt to decode the information. The Alamouti-based cooperative scheme proposed by Hua et al (2003) for flat-fading channels is modified in order work in the presence of multipath. A time-reversal distributed space-time block code (TR-DSTBC) is employed, which extends the classical TR-STBC approach from Lindskog and Paulraj (2000) to a cooperative communication scenario. Furthermore, the performance of the scheme employing a DFE equalizer at the destination is analytically investigated in terms of bit error rate (BER) bounds and achievable spatial diversity.

Space-time block codes have attracted recent interest due to their ability to take advantage of available diversity to transmit data over a wireless fading channel. Since they were first introduced, several strategies have been proposed for their design. In most cases, these designs were optimized for high SNR through a worst case pairwise error probability analysis and either placed strict constraints on the structure of codewords or were limited to codesets of low cardinality. This work addresses the issue of code design specifically for low SNR environments using union bound-based performance criteria which are SNR dependent. A more accurate union bound-based measure for performance evaluation of codes is developed and a variation of a locally optimum algorithm used to systematically construct good codeword sets is presented. New found codes are compared via simulation with other existing codes and are shown to exhibit improved performance.

A new criterion for performance evaluation of space-time block codes, based on the progressive union bound (PUB) is proposed. The PUB is not analytically tractable, in general, but can be well approximated by a saddlepoint approximation. The improvements provided by this new approach are illustrated by comparison with other bounds. New code sets, offering improved performance at low SNR, can also be found via the new bounds.