Detailed record: wireless usb protocol Broadband Analysis

Wireless technology is everywhere. Various wireless technologies, wireless Internet access methods, and wireless networks are emerging. Today, with the integration of "hot", various wireless networks are also integrated. Now we will introduce a new wireless technology: wireless USB. This article introduces the wireless USB protocol.

Certified wireless USB (CertifiedWirelessUSB) is a new technology that provides wireless connection capabilities built on a powerful wide media ultra-wideband (UWB) Public RF platform. WiMediaUWB can provide up to 480 Mb/s bandwidth, which is also the bandwidth of wired USB. Therefore, it attracts end users and application developers to migrate existing USB applications to the wireless field. USB wireless technology applications will benefit from portable hard drive, printers, digital cameras, and handheld devices such as PDAs or mobile phones.

Now people are concerned about how much effective bandwidth the new protocol can provide for applications or classdriver. Due to its wireless features, some additional components must be included in the total overhead. Can wireless USB provide sufficient bandwidth to support USB-enabled devices, especially those based on large structures and high bandwidth requirements? This article focuses on the efficiency of the wireless USB protocol. First, we will analyze in detail the wireless protocol overhead reduced to the frame level, and provide a simple comparison with USB as a reference. Next, we will study several application instances. Finally, we will briefly discuss potential bottlenecks in system implementation and possible solutions.

Cost Analysis of wireless USB protocol

Due to the features of wireless USB, it requires some "extra" Overhead compared with wired USB. Wireless USB is built on the WiMediaUWB platform. The platform includes a physical (PHY) layer of a point-to-point (adhoc) personal domain network (piconet, and a complete set of distributed Media Access Control (MAC) protocols. WiMediaMAC divides the time in the air into a basic Time Series Structure of 65 ms, called Ultra frame (super ). Then it is further divided into 256 Media Access gaps (mediumaccessslot ). Each superframe starts with a beaconperiod that accounts for 16 media gaps (MAS ). Beacon is at the core of WiMediaMAC; when every active WiMedia device tries to transmit its own beacon within the beacon cycle, it must listen to other beacon. In other words, 1/16 of the air time must be used for beacon operations over the WiMediaMAC protocol. In addition, the overhead of data packets, such as preamble, PHY, MAC header, And IFS, are inevitable. It should be noted that, even the best wired USB technology, is generally much smaller than wireless technology. Communication Method overhead also exists. A typical instance is "bit filling ". Similarly, from the application perspective, there are some parts that can be viewed as overhead at the data packet level, such as SYNC, EOP, and CRC.

Improvement of wireless USB protocol

To improve the efficiency of the wireless USB protocol, two methods are introduced to enhance the transaction type and traffic. In USB, a token from the USB host is required to pass in or out any data packet from a device. In wireless USB, data transmission is completed in the form of a transaction group. A transaction group is a combination of fine-tuning management commands (MMC) and the allocated protocol time gap. It executes one or more wireless USB transactions during the time gap. That is, for wireless USB, not every data packet transmitted in the air requires a token. A group of transactions targeting different endpoints (EP) pipelines (or even different devices) can share the same token.

The improvement of the Transfer Rate in wireless USB is achieved by defining a large package size (up to 3584 application load) and a burst mode of data. By using the data burst mode, the frame spacing can be reduced from 10us to 1.875us. In addition, the Emergency pilot (5.625us) can be used to replace the standard pilot (9.875us ). The topology of wireless USB generates a large amount of effective bandwidth. Due to its wireless features, the traditional "Tree" topology is no longer needed, so the hub is omitted. The time consumed by hub Round Robin can now be used for data transmission.

Finally, wireless USB is optimized in the advanced protocol. For example, for bulk-in transactions, wireless USB does not need a host to send an independent handshake packet, but embeds the handshake information in the subsequent MMC. This further improves the efficiency of the channel. Handshake is also omitted in the control transmission setting phase. If the data segment is followed by the control transmission, the Data Segment token is embedded into the set token.

From the above analysis, we can see that wireless USB can be seamlessly migrated to wireless USB due to its wireless characteristics and media access control layer. As for the greedy application of massive storage, the performance of wireless USB is somewhat affected than that of USB. In this case, further research is required to ensure that performance degradation is acceptable when a specific application or wireless solution is provided.

Implementation Suggestions

As mentioned above, the wireless USB protocol can achieve better bandwidth performance by transmitting batch data. The system designer should effectively manage the cache, that is, when the host provides a time window for data transmission (CTA) the device should always have enough data for sending or sufficient cache space for storing data. Cache management not only needs to consider application requirements, but also the end point pair Descriptor (endpoint companiondeor) of wireless USB ). Otherwise, the host still needs to arrange a Large Time Window Based on the package size and burst size. In fact, the device actually only takes some time. This will also waste the overall bus bandwidth.

Similarly, if a wireless USB host can accumulate multiple transaction requests from a higher level and efficiently organize them into transaction groups, the overall system performance of Multi-device configuration will be improved. Of course, the host implementation should have sufficient local cache to save the packets transmitted or received in the transaction group.