Zinan Lin

Haar Compression for Efficient CQI Feedback Signaling in 3GPP LTE Systems

Frequency selective scheduling is an attractive feature in the 3GPP LTE system that allows optimum usage of the allocated spectrum. In order to support frequency selective scheduling in the downlink, the mobile user needs to feedback channel quality indication (CQI) of the downlink channel to the base station. Several CQI feedback scheme have been proposed for 3GPP LTE systems. We propose to apply Haar compression to distributed subband groups to reduce the CQI feedback overhead. The simulation results indicate that the distributed- Haar scheme achieves the best trade-off between the throughput performance and overhead reduction compared with other CQI feedback schemes. We also observe that the sensitivity in sector throughput performance to user mobility is approximately the same for all feedback methods considered in the paper.

A comparison of MAC aggregation Vs. PHY bonding for WLANs in TV White Spaces

The availability of Television White Spaces (TVWS) has recently attracted considerable attention in industry and academia. Given the relatively small amount of bandwidth allocated to each TVWS channel (6, 7 or 8 MHz depending on geography), channel aggregation/bonding, which enables simultaneous usage of multiple TVWS channels, is an efficient approach to increasing the data rate. In this paper we compare channel aggregation at the MAC layer with channel bonding at the PHY layer. Three approaches are investigated: MAC layer aggregation, PHY layer bonding and a new proposal called enhanced PHY (ePHY) layer bonding. We present simulation results that show that when the SINR difference between aggregated/bonded channels is large that (i) the PHY performance of ePHY bonding is superior to PHY bonding both in terms of available data rates and PER performance and (ii) for both slow and fast link adaptation methodologies, ePHY bonding and MAC aggregation deliver higher throughputs than straightforward PHY bonding.

Relay Assisted Cooperative OSTBC Communication with SNR Imbalance and Channel Estimation Errors

In this paper, a two-hop relay assisted cooperative Orthogonal Space-Time Block Codes (OSTBC) transmission scheme is considered for the downlink communication of a cellular system, where the base station (BS) and the relay station (RS) cooperate and transmit data to the user equipment (UE) in a distributed fashion. We analyze the impact of the SNR imbalance between the BS-UE and RS-UE links, as well as the imperfect channel estimation at the UE receiver. The performance is analyzed in the presence of Rayleigh flat fading and our results show that the SNR imbalance does not impact the spatial diversity order. On the other hand, channel estimation errors have a larger impact on the system performance. Simulation results are then provided to confirm the analysis.

Full-Band CQI Feedback by Haar Compression in OFDMA Systems

Implementation of an efficient CQI feedback mechanism is the focus of the study presented in this paper. OFDMA-based systems such as 3GPP Long Term Evolution (LTE) downlink and WiMax require an accurate CQI feedback to allow effective operation of the adaptive modulation and coding. Besides accuracy, such mechanism should impose only a low overhead when using uplink resources for conveying the CQI information. Unlike the Best-M CQI feedback algorithms where only the M highest CQIs and their locations are reported, a full-band feedback method compresses the whole CQI vector and transmits the compressed vector in the uplink channel. In this paper, application of the Haar transform for a full-band CQI report is investigated and its performance is compared against Discrete Cosine Transform (DCT)-based compression schemes. Full-band Haar CQI feedback offers a flexible process for CQI feedback that can be easily adapted to different operating scenarios. Key features of Haar compression are incremental update and very low complexity for compression and decompression. Simulation results indicate that the full-band Haar scheme achieves significantly higher throughput than the DCT-based schemes at low speeds and about the same performance at higher speeds.

Link adaptation on aggregated TVWS channels

The availability of Television White Space (TVWS) [1] has attracted considerable attention in industry and academia. Given the relatively small amount of bandwidth allocated to each TVWS channel (e.g., 6, 7 or 8 MHz), and the non-contiguous nature of the availability, channel aggregation ([2], [3]) is an attractive way to make full use of the available TVWS spectrum and achieve higher throughput. In this paper we propose and analyze several link adaptation schemes in the context of MAC layer aggregation. We first analyze the SINR conditions of multiple aggregated channels using a model of a modified 802.11n system that supports TVWS operation. Then, we investigate three different link adaptation mechanisms and compute their MAC layer throughputs. Our results show that the SINR variance on the aggregated channels can be high, mainly due to the unique characteristics of TVWS spectrum, i.e., different maximum transmit powers imposed on different types of TVWS channels, and significant Digital TV (DTV) out-of-band emissions to adjacent TVWS channels. Both analytical and numerical results show that independent link adaptation based on each channel SINR provides much higher throughput than the single adaptation schemes, where a common rate is applied on the aggregated channels.

Performance analysis of different types of sensor networks for cognitive radios

We consider the problem of using multiple sensors to detect whether a certain spectrum is occupied or not. Each sensor sends its spectrum sensing result to a data fusion center, which combines all the results for an overall decision. With the existence of wireless fading on the channels from sensors to data fusion center, we examine three different mechanisms on the transmissions from sensors to data fusion center: (1) direct transmissions; (2) transmissions with the assistance of relays and (3) transmissions with the assistance of an intermediate fusion helper which fuses the sensing results from the sensors and sends the fused result to the data fusion center. For each mechanism, we analyze the correct probability of the overall decision made by the data fusion center. Our evaluation establishes that a sensor network with an intermediate fusion helper performs almost as good as a sensor network with relays, but providing energy and spectral advantages. Both networks significantly outperform the sensor network without relay or intermediate fusion helper. Such analysis facilitates the design of sensor networks. Furthermore, we generalize this evaluation to sensor networks with an arbitrary number of sensors and to sensor networks applying various information combining rules. Our simulations validate the analytical results.