Man Cheuk Ng

Airblue: a system for cross-layer wireless protocol development

Over the past few years, researchers have developed many crosslayer wireless protocols to improve the performance of wireless networks. Experimental evaluations of these protocols have been carried out mostly using software-defined radios, which are typically two to three orders of magnitude slower than commodity hardware. FPGA-based platforms provide much better speeds but are quite difficult to modify because of the way high-speed designs are typically implemented. Experimenting with cross-layer protocols requires a flexible way to convey information beyond the data itself from lower to higher layers, and a way for higher layers to configure lower layers dynamically and within some latency bounds. One also needs to be able to modify a layers processing pipeline without triggering a cascade of changes. We have developed Airblue, an FPGA-based software radio platform, that has all these properties and runs at speeds comparable to commodity hardware. We discuss the design philosophy underlying Airblue that makes it relatively easy to modify it, and present early experimental results.

Automatic synthesis of cache-coherence protocol processors using Bluespec

There are few published examples of the proof of correctness of a cache-coherence protocol expressed in an HDL. A designer generally shows the correctness of a protocol where many implementation details have been abstracted away. Abstract protocols are often expressed as a table of rules or state transition diagrams with an (implicit) model of atomic actions. There is enough of a semantic gap between these high-level abstract descriptions and HDLs that the task of showing the correctness of an implementation of a verified abstract protocol is as daunting as proving the abstract protocols correctness in the first place. The main contribution of this paper is to show that this problem can be largely avoided by expressing the verified abstract protocol in Bluespec SystemVerilog (BSV), which is based on guarded atomic actions and is synthesizable into efficient hardware. Consequently, once a protocol has been verified at the rules-level, little verification effort is needed to verify the implementation. We illustrate our approach by synthesizing a non-blocking MSI cache-coherence protocol for distributed memory systems and discuss the performance of the resulting implementation.

From WiFi to WiMAX: Techniques for High-Level IP Reuse across Different OFDM Protocols

Orthogonal frequency-division multiplexing (OFDM) has become the preferred modulation scheme for both broadband and high bitrate digital wireless protocols because of its spectral efficiency and robustness against multipath interference. Although the components and overall structure of different OFDM protocols are functionally similar, the characteristics of the environment for which a wireless protocol is designed often result in different instantiations of various components. In this paper, we describe how we can instantiate baseband processoring of two different wireless protocols, namely 802.11a and 802.16 in Bluespec from a highly parameterized code for a generic OFDM protocol. Our approach results in highly reusable IP blocks that can dramatically reduce the time-to-market of new OFDM protocols. One advantage of Bluespec over SystemC is that our code is synthesizable into high quality hardware, which we demonstrate via synthesis results. Using a Viterbi decoder we also demonstrate how parameterization can be used to study area-performance tradeoff in the implementation of a module. Furthermore, parameterized modules and modular composition can facilitate implementation-grounded algorithmic exploration in the design of new protocols.

A Comparative Evaluation of High-Level Hardware Synthesis Using Reed–Solomon Decoder

Using the example of a Reed-Solomon decoder, we provide insights into what type of hardware structures are needed to be generated to achieve specific performance targets. Due to the presence of run-time dependencies, sometimes it is not clear how the C code can be restructured so that a synthesis tool can infer the desired hardware structure. Such hardware structures are easy to express in an HDL. We present an implementation in Bluespec, a high-level HDL, and show a 7.8× improvement in performance while using only 0.45× area of a C-based implementation.

Design contest overview: Combined architecture for network stream categorization and intrusion detection (CANSCID)

This year we received 8 submissions for our Deep Packet Inspection problem. 6 submissions used FPGAs, and 2 used GP-GPUs. The organizers find it significant that no team submitted a software-only solution that did not use some kind of hardware accelerator— an indication that software alone could not meet the required line rate. This year the contest ended in a tie. Congratulations to the joint winners, Team Sasao Lab and Team Limenators, each having implemented 140 patterns while maintaining line rate. Additionally, Team Sasao Lab was the only team to use an NFA approach rather than DFAs for matching the regular expressions. Full results are given in Table II. The performance of the two winners was verified by the organizers using undisclosed test inputs. The performance of the other teams is self-reported.

High-throughput Pipelined Mergesort

We present an implementation of a high-throughput cryptosorter, capable of sorting an encrypted database of eight megabytes in .15 seconds; 1102 times faster than a software implementation.

WiLIS: Architectural modeling of wireless systems

The performance of a wireless system depends on the wireless channel as well as the algorithms used in the transceiver pipelines. Because physical phenomena affect transceiver pipelines in difficult to predict ways, detailed simulation of the entire transceiver system is needed to evaluate even a single processing block. Further, some protocol validations require simulation of rare events (say, 1 bit error in 109 bits), which means the protocol must simulate for a long enough time for such events to materialize. This requirement coupled with the heavy computation typical of most physical-layer processing, rules out pure software solutions. In this paper we describe WiLIS, an FPGA-based hybrid hardware-software system designed to facilitate the development of wireless protocols. We then use WiLIS to evaluate several microarchitectures for measuring very low bit-error rates (BER). We demonstrate, for the first time, that the recently proposed SoftPHY [16, 30] can be implemented efficiently in hardware.

A design flow based on modular refinement

We propose a practical methodology based on modular refinement to design complex systems. The methodology relies on modules with latency-insensitive interfaces so that the refinements can change the timing contract of a module without affecting the overall functional correctness of the system. Such refinements can exacerbate the unit testing problem for modules whose specifications admit a set of output behaviors for the same input (non-determinism), or modules whose input behavior may be affected by past outputs (feedback). We avoid the difficult problem of generating appropriate unit tests for such modules by using system-level tests as unit tests to verify the correctness of refined modules. We illustrate our methodology by showing how one might develop a microprocessor with an in-order pipeline. We then develop a superscalar pipeline using the in-order pipeline as the starting point. Our methodology leverages the effort of design exploration to reduce the effort of specifying interface contracts and unit testing.

Implementing a fast cartesian-polar matrix interpolator

The 2009 MEMOCODE Hardware/Software Co-Design Contest assignment was the implementation of a cartesian-to-polar matrix interpolator. We discuss our hardware and software design submissions.