This paper presents the design, implementation and evaluation of Picasso, a novel radio design that allows simultaneous transmission and reception on separate and arbitrary spectrum fragments using a single RF frontend and antenna. Picasso leverages this capability to flexibly partition fragmented spectrum into multiple slices that share the RF frontend and antenna, yet operate concurrent and independent PHY/MAC protocols. We show how this capability provides a general and clean abstraction to exploit fragmented spectrum in WiFi networks, handle coexistence in dense deployments as well as many other applications. We prototype Picasso, and demonstrate experimentally that a Picasso radio partitioned into four slices, each concurrently operating four standard WiFi OFDM PHY and CSMA MAC stacks, can achieve the same sum throughput as four physically separate radios individually configured to operate on the spectrum fragments. We also demonstrate experimentally how Picasso's slicing abstraction provides a clean mechanism to enable multiple diverse networks to coexist and achieve higher throughput, better video quality and latency than the best known state of the art approaches.

Many applications can benefit from the capability to simultaneously and independently use arbitrarily sized but separate spectrum fragments with a single radio and antenna. By this capability we mean that the radio can simultaneously transmit, simultaneously receive, or simultaneously transmit and receive on arbitrary but separate spectrum fragments. For example, we can use it for spectrum aggregation in fragmented ISM bands as shown in as shown in Fig. 2(A). A WiFi AP can run independent OFDM PHY and CSMA MAC protocols on two WiFi channels to simultaneously serve two legacy WiFi clients assigned to different channels and achieve significantly higher throughput than a legacy AP that is restricted to use only one channel at a time. Similarly, a WiFi client radio with such a capability can use it to simultaneously connect to multiple WiFi APs on different channels and obtain a much higher aggregate throughput than current radios that can transmit or receive on only one channel at a time.

Wireless spectrum is increasingly fragmented due to the growing proliferation of unlicensed wireless devices and piecemeal licensed spectrum allocations. Current radios are ill-equipped to exploit such fragmented spectrum since they expect large contiguous chunks of spectrum to operate on. In this paper we argue that future radios should provide full duplex signal shaping to the higher layers to systematically exploit fragmented spectrum. Such an architectural design would allow the radio to decouple the use of different spcetrum fragments. We present the design and implementation of Picasso, a system that provides such a general signal shaping abstraction. Picasso has two novel components: a self-interference cancellation technique and a programmable filter engine that enables it to simultaneously send and receive over different spectrum fragments. We provide an initial design and empirically evaluate the feasibility of both components.

The ability to detect what unlicensed radios are operating in a neigh borhood, their spectrum occupancies and the spatial directions their signals are traversing is a fundamental primitive needed by many applications, ranging from smart radios to coexistence to network management to security. In this paper we present DOF, a detector that in a single framework accurately estimates all three parameters. DOF builds on the insight that in most wireless protocols, there are hidden repeating patterns in the signals that can be used to construct unique signatures, and accurately estimate signal types and their spectral and spatial parameters. We show via experimental evaluation in an indoor testbed that DOF is robust and accurate, it achieves greater than 85% accuracy even when the SNRs of the detected signals are as low as 0 dB, and even when there are multiple interfering signals present. To demonstrate the benefits of DOF, we design and implement a preliminary prototype of a smart radio that operates on top of DOF, and show experimentally that it provides a 80% increase in throughput over Jello, the best known prior implementation, while causing less than 10% performance drop for co-existing WiFi and Zigbee radios.