Multiuser MIMO Systems

HybridCast: Joint Multicast-Unicast Design for MU-MIMO Networks
Wireless standards, e.g., LTE and 802.11ac, have not specified MIMO communications for multicasting. Existing systems hence simply allow a single multicast transmission, as a result underutilizing the multiple antennas at a base-station. Even worse, in most of systems, multicast is by default sent at the base rate, wasting a considerable link margin available for delivering extra information. To address this inefficiency, we present HybridCast, a MU-MIMO system that enables joint unicast and multicast. HybridCast efficiently leverages the unused MIMO capability and link margin to send unicast streams concurrently with a multicast session.
SIEVE: Scalable User Grouping for MU-MIMO Systems
How to select users into a beamforming group becomes the bottleneck of realizing the MU-MIMO gain. The fundamental challenge for user selection is the large searching space, and hence there exists a tradeoff between search complexity and achievable capacity. We present a novel MU-MIMO user grouping system, called SIEVE. The key invention is a knob that controls the aggressiveness in searching the best beamforming group. SIEVE hence naturally moves between the two extremes: exhaustive search and random search, adapting to channel dynamics and available computational power.
MIMOMate: Leader-Contention-Based MU-MIMO User Matching
Existing MU-MIMO systems exploit the traditional 802.11 contention to allocate concurrent transmission opportunities on the uplink. Such a contention-based protocol not only wastes channel time on multiple rounds of contention, but also fails to maximally deliver the gain of MU-MIMO. We introduces MIMOMate, a leader-contention-based MU-MIMO MAC protocol that matches clients as concurrent transmitters according to their channel correlation. Furthermore, MIMOMate elects the leader of the matched users to contend using 802.11 CSMA/CA. It hence requires only a single contention overhead for concurrent streams, and can be compatible with legacy 802.11 devices.
TurboRate: Rate Adaptation for 802.11 Multiuser MIMO Networks
In multiuser MIMO (MU-MIMO) networks, the optimal bit rate of a user is highly dynamic and changes from one packet to the next. This breaks traditional bit rate adaptation algorithms, which rely on recent history to predict the best bit rate for the next packet. We introduce TurboRate, a rate adaptation scheme for MU-MIMO LANs. TurboRate shows that a client can adapt the bit rate on a per-packet basis based on the channels of its concurrent clients. A Turborate client can achieve this goal by learning two variables passively, its SNR and the direction along its signal received at the AP, without exchanging control frames with the access point.
802.11n+: Random Access Heterogeneous MIMO Networks
802.11n+ is a fully distributed random access protocol for MIMO networks. It allows nodes that differ in the number of antennas to contend not just for time, but also for the degrees of freedom provided by multiple antennas. We show that even when the medium is already occupied by some nodes, nodes with more antennas can transmit concurrently without harming the ongoing transmissions. Furthermore, such nodes can contend for the medium in a fully distributed way. [paper] [slide] [project webpage]

Wireless Systems

ZipTx: Hiarnessing Partial Packets in 802.11 Networks
ZipTx explores ways to take advantage of partial packets to improve throughput. In 802.11 networks, when packets are lost, often most of the bits are received fully correctly. We find that, instead of throwing away corrupted packets, a system can achieve a higher throughput if we can retain them and try to correct their faulty bits. In addition, ZipTx modifies the autorate algorithm to account for partially received packets, allowing it to push to higher bit rates while still running reliably.
FatVAP: Aggregating AP Backhaul Bandwidth
FatVAP is an 802.11 driver that aggregates the bandwidth available at accessible APs and also balances user load across the APs. FatVAP has three key features. First, it knows exactly how long to connect to each AP in order to collect the bandwidth it can ever get from this AP. Second, FatVAP switches quickly between APs and without losing queued packets, making it the only driver that can sustain concurrent high throughput TCP connections across multiple APs. Third, FatVAP works with unmodified APs and is transparent to applications and the rest of the network stack.

Network Planning

Sink Deployment in Wireless Camrea Networks
Multi-Rate Multi-Channel Wireless Mesh Networks

Multimedia Networks

Quality-Differentiated Wireless Multicasting
SocioNet: Social-based P2P Content Search
 
 
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