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We address the problem of precoding in downlink multi-user MIMO communications using SDMA. In this setup, multiple antennas are used at the base station and at the terminals. A double level of spatial multiplexing is present: the users are spatially multiplexed (SDMA) and each user receives spatially multiplexed symbol streams (SDM). The cumulative multi-user and multi-stream interference is a potential...
This paper describes the implementation of a flexible combined binary and non-binary LDPC decoder. The ASIP architecture can be configured allowing re-use between both modes. Key in the architecture is parallelization, which is exploited in the SIMD engine. Binary LDPC codes intrinsically enables parallelization through layered decoding while in the non-binary case different trade-offs can be made...
Soft output demapping is crucial for emerging standards with Turbo or LDPC FEC schemes. Existing soft output demapping techniques incur several problems when implementing on state of the art baseband processors: (1) too many operations, the number of average operation per-bit is even higher than that of FFTs; (2) difficult to exploit the potential parallelism supported by baseband processors; (3)...
This paper describes the implementation of a flexible Turbo and LDPC outer modem engine which is capable of supporting the WiFi(802.11n), WiMax(802.16e) and 3GPPLTE standard on the same hardware resources. The chip is implemented in a 65 nm CMOS technology and occupies 10.37 mm2. The decoder flexibility is offered by means of an application-specific instruction-set processor (ASIP), with full datapath...
Wireless communication standards are developed at an ever-increasing rate of pace, and significant amounts of effort is put into research for new communication methods and concepts. On the physical layer, such topics include MIMO, cooperative communication, and error control coding, whereas research on the medium access layer includes link control, network topology, and cognitive radio. At the same...
Reducing the energy consumption is one of the most demanding design targets for mobile devices. To this end, we develop a 3GPP-LTE cross-layer design that combines the functionality of Media Access Control (MAC) and Physical (PHY) layers with the power consumption of the hardware platform components to achieve an optimized solution in terms of energy consumption. Models for the baseband, the hardware,...
This paper optimizes handover decisions between WLAN (802.11) and WiMAX (802.16e) standards, for both uplink and downlink data transmission. The handover becomes part of a cross-layer approach controlling several knobs (air interface parameters or platform settings) in order to reduce the terminal power consumption. The first step is to derive detailed power and performance models for both standards,...
The success of dynamic spectrum access through simple listen-before-talk etiquettes has paved the way for opening up the spectrum. However, many problems still remain in these networks. Due to the complex nature of IEEE 802.11 networks, for instance, optimizing these networks regarding power, rate and carrier sense threshold remains a very tough challenge. In this paper, we introduce spatial learning...
The scalable video coding extends the H.264/AVC video coding standard by providing temporal, spatial and quality scalability. A set of new tools, such as key picture and inter-layer prediction are introduced in SVC to improve either rate-distortion performance or error resilience. This paper evaluates the impact of these tools on the performance of an optimized SVC decoder, in terms of rate, distortion,...
Wireless communication standards are continuously evolving and getting more diverse.This requires a wide variety of baseband implementations within a short time-to-market. Besides, deep sub-micron technology significantly increases the design complexity and associated cost. These yield a growing need for reconfigurable/programmable baseband solutions. Implementing the whole base band functionality...
A major limitation for wireless video communication over portable devices is the limited energy supply. For this reason, an efficient energy usage becomes a critical issue. In this paper we focus on the energy minimization of the two main energy consumers at the device: video encoding and wireless communication tasks. For this purpose, we develop a cross-layer approach that explores the tradeoff between...
Achieving low energy consumption is one of the main challenges for wireless video transmission on battery-limited devices. Moreover, the bandwidth is scarce and must be shared efficiently among users. The focus in this paper is on the timely delivery of multiple delay-sensitive video flows over a distributed access wireless LAN with minimal energy cost. This is done taking into consideration the Enhanced...
Software Defined Radio (SDR) terminals are crucial to enable seamless and transparent inter-working between fourth generation wireless access systems or communication modes. On the longer term, SDRs will be extended to become cognitive radios enabling efficient spectrum usage. Future communication modes will have heavy hardware resource requirements and switching between them will introduce dynamism...
The success of dynamic spectrum access through simple listen-before-talk etiquettes has made way for opening up the spectrum. However, many problems still remain in this kind of networks. Stations might not be able to sense as much transmissions and hence defer channel access less often than their neighbors. This can lead to unfairness or (worst-case) starvation of certain terminals. In this paper...
Thanks to recent advances in wireless technology, a broad range of standards are currently emerging. Interoperability and coexistence between these heterogeneous networks are becoming key issues, which require new adaptation strategies to avoid harmful interference. In this paper, we focus on the coexistence of 802.11 WLANs and 802.15.4 sensor networks in the ISM band. These networks have very different...
In this paper, we propose a cross-layer optimization scheme for multi-user video streaming over the uplink of IEEE 802.11e HCCA wireless network. The objective is to minimize the energy consumption of all users, including both video encoder energy and wireless transmission energy, while delivering desired video quality for each user. In our proposed scheme, both cross-layer optimization of individual...
A cognitive radio (CR) network should be able to sense its environment and adapt its communication to utilize unused licensed spectrum without interfering with incumbents. Properly modeling the expected interference from the CR network is therefore very important in the definition of coexistence rules to efficiently protect the incumbents. In this paper we model the accumulative interference generated...
In the design of modern mobile wireless networks the effort for performance improvement has to be balanced with the effort in more effective energy management strategies. In fact, the capacity of batteries is not increasing as new devices and multimedia applications requires. In this paper a new approach to routing optimization in ad-hoc wireless networks supporting multimedia communication is investigated...
Wireless access schemes was implemented on software defined radios (SDRs) in the future. In mobile terminals, SDRs should couple a high functional flexibility to low power operation. A two-step approach is advocated in this context. First, energy-scalability is introduced in the SDR design. Secondly, intelligent run-time cross-layer control is introduced to enable low power operation, by exploiting...
Achieving low energy consumption is one of the main challenges for wireless video transmission on battery limited devices. Moreover, the bandwidth is scarce and needs to be properly shared amongst different users. Congestion in the network can result in packet losses, with a significant impact on video quality. In this paper we propose the use of a channel-adaptive rate control mechanism in a multi-user...
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