Linear Precoders for Non-Regenerative Asymmetric Two-way Relaying in Cellular Systems

Two-way relaying (TWR) reduces the spectral-efficiency loss caused in conventional half-duplex relaying. TWR is possible when two nodes exchange data simultaneously through a relay. In cellular systems, data exchange between base station (BS) and users is usually not simultaneous e.g., a user (TUE) has uplink data to transmit during multiple access (MAC) phase, but does not have downlink data to receive during broadcast (BC) phase. This non-simultaneous data exchange will reduce TWR to spectrally-inefficient conventional half-duplex relaying. With infrastructure relays, where multiple users communicate through a relay, a new transmission protocol is proposed to recover the spectral loss. The BC phase following the MAC phase of TUE is now used by the relay to transmit downlink data to another user (RUE). RUE will not be able to cancel the back-propagating interference. A structured precoder is designed at the multi-antenna relay to cancel this interference. With multiple-input multiple-output (MIMO) nodes, the proposed precoder also triangulates the compound MAC and BC phase MIMO channels. The channel triangulation reduces the weighted sum-rate optimization to power allocation problem, which is then cast as a geometric program. Simulation results illustrate the effectiveness of the proposed protocol over conventional solutions.Comment: 30 pages, 7 figures, submitted to IEEE Transactions on Wireless Communication

Broadband wireless technology for rural India

168-171Broadband services can be best provided in rural India using wireless technology. Given modest income levels, internet-based services are accessible to most of the rural populace only through a kiosk model of delivery. Such services call for a wireless system that can provide at least 256 kbps in a sustained manner, to each of around 200 villages within a radius of 20 km from an Internet POP (Post Office Protocol). The challenge, however, is to do this at a cost per connection of under US$ 250 for the wireless equipment, in order to make the kiosk a viable business. Emerging wide-area broadband wireless technologies such as those based on the IEEE 802.16 (WiMAX) standard, when mature, may meet these performance and cost requirements. If broadband services are to be provided today, and at an affordable cost, one has to look for innovative ways of adapting low-cost, high bit-rate, and high-capacity technologies meant for local networks. Two standards that are amenable to such adaptation are DECT and IEEE 802.11 (WiFi), and Broadband corDECT and WiFiRe systems are, respectively, examples thereof. The corDECT system has been proven in rural deployments and shown to provide a feasible solutio

Efficient Low Bit-Rate Low-Latency Channelization in DECT

In a TDMA standard such as DECT, low bit-rate transmission is feasible either at the cost of efficiency (shorter slots with fixed overhead per slot) or increased latency (longer frames). This paper proposes a new scheme for low bit-rate low-latency channelization in the DECT standard, in which data can be efficiently transmitted at rates as low as 10 kbps. This could be useful for sending acknowledgments for a high-speed data communication link, or for vocoder/VoIP traffic. The proposed scheme enables efficient low bit-rate transmission by dividing a DECT channel into four subbands, and by employing a new slot structure wherein TDMA overhead is kept to a minimum. It is shown that the proposed scheme can coexist with the DECT system and can be implemented using existing IMT-2000 DECT hardware with minor modifications. A comparison is also made of the proposed scheme with existing options for low bit-rate channelization in DECT.</p

Robust LLR aided Low Feedback Precoding for Interference Alignment

Abstract-Interference alignment, as proposed i

Deploying IP multimedia subsystem (IMS) services over next generation networks (NGNs) : the IU-ATC integrated test bed

The IP Multimedia Subsystem (IMS) is the Third Generation Partnership Project’s (3GPP) standardized service platform that enables the deployment of rich and personalized services over fixed and mobile networks whilst allowing end-users ubiquitous access to services such as voice, video, presence and online gaming anytime and anywhere. However, the delivery of these services to the end-users is highly dependent on the available or preferred access network which could range from fixed broadband access to mobile 4G connections. Although the IMS was initially developed as the core network for Third Generation (3G) systems, it has now been adopted as the service platform for the Long Term Evolution (LTE) and System Architecture Evolution (SAE). As this transition of 3G to 4G and beyond evolves, there is an immediate need for a research testbed that facilitates the research, development and early trials of the integration of these technologies. This has motivated us to integrate the IMS based Advanced Next Generation Network (ANGN) testbed at the University of Surrey (UniS), U.K. with the 4G Access Network Testbed at IIT Madras, India via an academic transnational network link to form a fully functional telecommunications mobile network. In this paper, we discuss the rationales, motivations and objectives behind the integrated testbed whilst also investigating how it can be extended to support 4G and future technologies such as LTE/SAE and WiMAX. The testbed as a whole plays a key as role in the future of IMS development as it provides a fully functional platform similar to commercial networks for researchers to investigate and demonstrate the feasibility of their proposal in a realistic environment