Wireless local area networks (W-LANs) have become increasingly popular due to the recent availability of affordable devices that are capable of communicating at high data rates. These high rates are possible, in part, through new modulation schemes that are optimized for the channel conditions bringing about a dramatic increase in bandwidth efficiency. Since the choice of which modulation scheme to use depends on the current state of the transmission channel, newer wireless devices often support multiple modulation schemes, and hence multiple datarates, with mechanisms to switch between them Users are given the option to either select an operational datarate manually or to let the device automatically choose the appropriate modulation scheme (data rate) to match the prevailing conditions. Automatic rate selection protocols have been studied for cellular networks but there have been relatively few proposals for W-LANs. In this paper we present a rate adaptive MAC protocol called the Receiver-Based AutoRate (RBAR) protocol. The novelty of RBAR is that its rate adaptation mechanism is in the receiver instead of in the sender. This is in contrast to existing schemes in devices like the WaveLAN II [15]. We show that RBAR is better because it results in a more efficient channel quality estimation which is then reflected in a higher overall throughput Our protocol is based on the RTS/CTS mechanism and consequently it can be incorporated into many medium access control protocols including the widely popular IEEE 802.11 protocol. Simulation results of an implementation of RBAR inside IEEE 802.11 show that RBAR performs consistently well.

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A rate-adaptive MAC protocol for multi-Hop wireless networks

In a data communication system capable of variable rate transmission, high rate packet data transmission improves utilization of the forward link and decreases the transmission delay. Data transmission on the forward link is time multiplexed and the base station transmits at the highest data rate supported by the forward link at each time slot to one mobile station. The data rate is determined by the largest C/I measurement of the forward link signals as measured at the mobile station. Upon determination of a data packet received in error, the mobile station transmits a NACK message back to the base station. The NACK message results in retransmission of the data packet received in error. The data packets can be transmitted out of sequence by the use of sequence number to identify each data unit within the data packets.

Method and apparatus for high-rate packet data transmission

Techniques to process data for transmission over a set of transmission channels selected from among all available transmission channels. In an aspect, the data processing includes coding data based on a common coding and modulation scheme to provide modulation symbols and pre-weighting the modulation symbols for each selected channel based on the channel's characteristics. The pre-weighting may be achieved by “inverting” the selected channels so that the received SNRs are approximately similar for all selected channels. With selective channel inversion, only channels having SNRs at or above a particular threshold are selected, “bad” channels are not used, and the total available transmit power is distributed across only “good” channels. Improved performance is achieved due to the combined benefits of using only the NS best channels and matching the received SNR of each selected channel to the SNR required by the selected coding and modulation scheme.

Method and apparatus for processing data for transmission in a multi-channel communication system using selective channel inversion

Techniques for transmitting data from a transmitter unit to a receiver unit in a multiple-input multiple-output (MIMO) communication system. In one method, at the receiver unit, a number of signals are received via a number of receive antennas, with the received signal from each receive antenna comprising a combination of one or more signals transmitted from the transmitter unit. The received signals are processed to derive channel state information (CSI) indicative of characteristics of a number of transmission channels used for data transmission. The CSI is transmitted back to the transmitter unit. At the transmitter unit, the CSI from the receiver unit is received and data for transmission to the receiver unit is processed based on the received CSI.

Method and apparatus for utilizing channel state information in a wireless communication system

The object is achieved by providing a base station apparatus for performing time and frequency scheduling in uplink packet access with: an interference amount measurement part configured to measure an uplink interference amount for each interference amount measurement unit which comprises a predetermined period and a predetermined number of frequency blocks; an interference amount determination part configured to determine whether the uplink interference amount satisfies a predetermined condition; and an overload indicator reporting part configured to report an overload indicator to a neighboring cell when the predetermined condition is satisfied.

Base station apparatus and communication control method

We propose a technique to measure channel quality in terms of signal-to-interference plus noise ratio (SINR) for the transmission of signals over fading channels The Euclidean distance (ED) metric, associated with the decoded information sequence or a suitable modification thereof, is used as a channel quality measure Simulations show that the filtered or averaged metric is a reliable channel quality measure which remains consistent across different coded modulation schemes and at different mobile speeds The average scaled ED metric can be mapped to the SINR per symbol We propose the use of this SINR estimate for data rate adaptation, in addition to mobile assisted handoff (MAHO) and power control We particularly focus on data rate adaptation and propose a set of coded modulation schemes which utilize the SINR estimate to adapt between modulations, thus improving the data throughput Simulation results show that the proposed metric works well across the entire range of Dopplers to provide near-optimal rate adaptation to average SINR This method of adaptation averages out short-term variations due to Rayleigh fading and adapts to the long-term effects such as shadowing At low Dopplers, the metric can track Rayleigh fading and match the rate to a short-term average of the SINR, thus further increasing throughput

Channel quality estimation and rate adaptation for cellular mobile radio

A multiple mode data communication system and method provides the flexibility to schedule wireless unit transmissions and/or allow the wireless unit to transmit autonomously. In certain embodiments, the wireless units can transmit autonomously and/or use scheduling depending on the data rate, the length of the data packet or the type of data. For example, the wireless units can transmit autonomously at lower data rates and use scheduling at higher data rates. Thus, the multiple mode system enables wireless unit transmissions to be scheduled and/or be transmit autonomously, and wireless units can simultaneously operate in different scheduling and/or autonomous modes. Depending on the embodiment, the system can provide even greater flexibility in operation by permitting wireless units to be scheduled by a single base station, scheduled by a multiplicity of base stations simultaneously or otherwise, via coordination between base stations, scheduled by a multiplicity of base stations in an uncoordinated and asynchronous manner, allowed to transmit autonomously, and/or allowed to transmit autonomously under base station supervision (i.e. rate control/adjustment by the base station). Additionally, a forward and/or reverse link control channel structure is provided which can be used to implement the multiple mode data communication system and/or support various features enabling increased throughput over a shared data channel in a wireless communications system.

Multiple mode data communication system and method and forward and/or reverse link control channel structure

A system and method to measure channel quality in terms of signal to noise ratio for the transmission of coded signals over fading channels. A Viterbi decoder metric for the Maximum Likelihood path is used as a channel quality measure. This Euclidean distance metric is filtered in order to smooth out short term variations. The filtered or averaged metric is a reliable channel quality measure which remains consistent across different coded modulation schemes and at different mobile speeds. The filtered metric is mapped to the signal to noise ratio per symbol using a threshold based scheme. Use of this implicit signal to noise ratio estimate is used for the mobile assisted handoff and data rate adaptation in the transmitter.

System and method for measuring channel quality information

Packet data is expected to dominate third generation wireless networks, unlike current generation voice networks. This opens up new and interesting problems. Physical and link layer issues have been studied extensively, while resource allocation and scheduling issues have not been addressed satisfactorily.In this work, we address resource management on the downlink of CDMA packet data networks. Network performance (for example, capacity) has been addressed, but user centric performance has not received much attention. Recently, various non-traditional scheduling schemes based on new metrics have been proposed, and target user performance (mostly without reference to wireless). We adapt these metrics to the CDMA context, and establish some new results for the offline scheduling problem. In addition, we modify a large class of online algorithms to work in our setup and conduct a wide range of experiments. Based on detailed simulations, we infer that: Algorithms which exploit “request sizes” seem to outperform those that do not. Among these, algorithms that also exploit channel conditions provide significantly higher network throughput.Depending on continuous or discretized bandwidth conditions, either pure time multiplexing or a combination of time and code multiplexing strikes an excellent balance between user satisfaction and network performance.Discrete bandwidth conditions can lead to degraded user level performance without much impact on network performance. We argue that the discretization needs to be fine tuned to address this shortcoming.

Downlink scheduling in CDMA data networks

In a wireless network or other communication system, admission of users to the system involves use of a first scheduler, which makes actual scheduling decisions for admitted users, and a second scheduler, which emulates the operation of the first scheduler. The first scheduler is configured to manage access to network resources for users already admitted to the system. The first scheduler is coupled to an admission control module which contains the second scheduler. The second scheduler, also referred to herein as a virtual scheduler, emulates operation of the first scheduler, under an operating scenario involving admission of at least one additional user to the system, in order to generate a performance metric. The performance metric is used to make an admission control decision regarding admission of the at least one additional user to the system.

Srinivas R. Kadaba

Papers

Channel quality estimation and rate adaptation for cellular mobile radio

Multiple mode data communication system and method and forward and/or reverse link control channel structure

System and method for measuring channel quality information

Downlink scheduling in CDMA data networks

Method and apparatus for quality-of-service based admission control using a virtual scheduler