Wireless USB is a wireless technology which enables the high speed computer peripheral interface, USB, wireless. It is a wire replacement of existing USB technology using a Multi Band Orthogonal Frequency Division Multiplexing radio technique.Wireless USB is a logical bus that supports data exchange between a host device (typically a PC) and a wide range of simultaneously accessible peripherals. The attached peripherals share bandwidth through a host-scheduled, TDMA-based protocol. The bus allows peripherals to be attached, configured, used, and detached while the host and other peripherals are in operation. Security definitions are provided to assure secure associations between hosts and devices, and to assure private communication.
Wireless USB connects USB devices with the USB host using a 'hub and spoke' model. The Wireless USB host is the 'hub" at the center, and each device sits at the end of a 'spoke'. Each 'spoke' is a point-to-point connection between the host and device. Wireless USB hosts can support up to 127 devices and because Wireless USB does not have physical ports there is no need, nor any definition provided,
Wireless USB is a wireless technology which enables the high speed computer peripheral interface, USB, wireless. It is a wire replacement of existing USB technology using a Multi Band Orthogonal Frequency Division Multiplexing radio technique.
Wireless USB interest group was formed in 2004. It is the first high speed personal interconnect. The physical layer is standardized under IEEE 802.15.3 PHY. Today it is in the developing stage. The major WUSB promoters are HP, Intel, Microsoft, NEC Philips, & Samsung
A USB system consists of a host and some number of devices all operating together on the same time base and the same logical interconnect. A USB system can be described by three definitional areas:
• USB interconnect
• USB devices
• USB host
The USB interconnect
The USB interconnect is the manner in which USB devices are connected to and communicate with the host. USB devices
Wireless USB devices are one of the following:
Functions, which provide capabilities to the system, such as a printer, a digital camera, or speakers
Device Wire Adapter, which provides a connection point for wired USB
devices.
USB Host
There is only one host in any USB system. The USB interface to the host computer system is referred to as the Host Controller. Host controllers are typically connected to PCs through an internal bus such as PCI. The Host Controller may be implemented in a combination of hardware, firmware, or software.
Wireless USB has an advanced power management system which consumes very low power. The power management system is based on Tx/Rx system. It also supports an advanced encryption system in order to ensure the secure connection between the host and device.
2. NEED FOR ANOTHER WIRELESS TECHNIQUE
USB is a fast growing technology and now above 80% of all devices supports USB connectivity to a PC. It will be a great reduce of number of wires and cost for paying the cables, if the existing USB technique goes wireless.
Today, an office PC is disturbed with rat's nest of cables. By adopting the current wireless technology such as Bluetooth, WiFi, ZigBee, IR, etc doesn't reduces the number of wires since they have not enough bandwidth to support bigger data transfer rate.
A survey reveals the requirements of bandwidth for different devices, which is shown in the table below.
| Peripheral | Desired BW | Comments |
| Video conf & digital still cameras | 75-150Mbps | MPEG-2 quality w/o compression; roll download in seconds not minutes. |
| Scanners | 50-100Mbps+ | Faster, high resolution scan |
| Printers | 50-100Mbps+ | Higher resolutions, more colors, or elimination of line/page buffers allows lower cost |
| External storage | Up to 240Mbps | SCSI/IDE performance levels. CD/ RW, DVD-RAM, HDD, flash memory |
| Broadband | 10-1000Mbps | Cable, DSL, Ethernet, HPNA, ... |
| High resolution monitors, projectors | 63Mbps+ | Upper limit (to ~4Gbps) a function of tolerable compression |
Wireless USB support a high bandwidth of 480Mbps and it's scalable architecture extends the bandwidth up to lGbps.Moreover it is much less costly than Bluetooth and consumes much less power than any other wireless device.
Wireless USB supports both PC as well as personal Consumer Electronics devices such as audio/video players.
Wireless USB supports a mixture of both high speed and low speed devices and can be operated in multiple data transfer rates.
3. ARCHITECTURAL OVERVIEW
Wireless USB is a logical bus that supports data exchange between a host device (typically a PC) and a wide range of simultaneously accessible peripherals. The attached peripherals share bandwidth through a host-scheduled, TDMA-based protocol. The bus allows peripherals to be attached, configured, used, and detached while the host and other peripherals are in operation. Security definitions are provided to assure secure associations between hosts and devices, and to assure private communication.
3.1 USB System Description
A USB system consists of a host and some number of devices all operating together on the same time base and the same logical interconnect. A USB system can be described by three definitional areas:
• USB interconnect
• USB devices
■
• USB host
3.1.1 USB interconnect
The USB interconnect is the manner in which USB devices are connected to and communicate with the host. This includes the following:
• Topology
• Data Flow Models
• USB Schedule
3.1.1.1 Topology
Wireless USB connects USB devices with the USB host using a 'hub and spoke' model. The Wireless USB host is the 'hub' at the center, and each device sits at the end of a 'spoke'. Each 'spoke' is a point-to-point connection between the host and device Wireless USB hosts can support up to 127 devices and because Wireless USB does not have physical ports there is no need, nor any definition provided, for hub devices to provide port expansion. The figure illustrates the topology system
3.1.1.2 Data Flow Models
The manner in which data moves in the system over the USB between producers and consumers.
3.1.1.3 USB Schedule
The USB provides a shared interconnect. Access to the interconnect is scheduled in order to support isochronous data transfers and to eliminate arbitration overhead.
3.1.2 USB Devices
Wireless USB devices are one of the following:
Functions, which provide capabilities to the system, such as a printer, a digital camera, or speakers
• Device Wire Adapter, which provides a connection point for wired USB devices. Wireless USB devices present a standard USB interface in terms of the following:
• Their comprehension of the Wireless USB protocol
• Their response to standard USB operations, such as configuration and reset
3.1.3 USB Hosts
There is only one host in any USB system. The USB interface to the host computer system is referred to as the Host Controller. Host controllers are typically connected to PCs through an internal bus such as PCI. The Host Controller may be implemented in a combination of hardware, firmware, or software. This specification defines another way that a host controller may be 'connected' to a PC. Chapter 8 describes a Wire Adapter device class that allows USB host functionality to be connected to a PC through a USB connection (either wired or wireless). Wire Adapters that directly connect to the PC using wired USB are known as Host Wire Adapters. Host Wire Adapters add Wireless USB capability to a PC. Wire Adapters that are Wireless USB devices and hence connect to the PC wirelessly are known as Device Wire Adapters. Device Wire Adapters typically have USB 'A' connectors (i.e. they look like wired hubs) and allow wired USB devices to be connected wirelessly to a host PC. Note that each Wire Adapter creates a new 'USB system', in that there is one host (the wire adapter) talking to one or more devices using the same time base and interconnect. Wire Adapters are important enabling devices for Wireless USB. Host Wire Adapters enable existing PCs to support Wireless USB. Device Wire Adapters allow existing wired USB devices to have a wireless connection to the host PC.
3.2 Physical Interface
Physical layer of Wireless USB is described in the Multi band OFDM Alliance (MBOA) UWB PHY specification, see reference [4]. The PHY supports information data rates of 53.3, 80, 106.7, 200, 320, 400 and 480 Mb/s and multiple channels. The PHY also provides appropriate error detection and correction schemes to provide as robust a communication channel as possible. For Wireless USB devices, the support of transmitting and receiving data at rates of 53.3, 106.7, and 200 Mb/s is mandatory. The support for the remaining data rates of 80, 160, 320, 400 and 480 Mb/s is optional. Wireless USB Hosts are required to support all data rates for both transmission and reception. All Wireless USB
3.3 Power Management
A Wireless USB host may have a power management system that is independent of the USB. The USB System Software interacts with the host's power management system to handle system power events such as suspend or resume. Additionally, USB devices typically implement additional power management features that allow them to be power managed by system software. This specification defines mechanisms and protocols that allow hosts and devices to be as power efficient as possible.
3.4 Bus Protocol
Logically, Wireless USB is a polled, TDMA based protocol, similar to wired USB. The Host Controller initiates all data transfers. Like wired USB, each transfer logically consists of three 'packets': token, data, and handshake. However, to increase the usage efficiency of the physical layer by eliminating costly transitions between sending and receiving, hosts combine multiple token information into a single packet. In that packet, the host indicates the specific time when the appropriate devices should either listen for an OUT data packet, or transmit an IN data packet or handshake (see Figure 3-2).
3.5 Robustness
There are several attributes of wireless USB that contribute to its robustness:
The physical layer, defined by [4], is designed for reliable communication and robust error detection and correction.
• Detection of attach and detach and system-level configuration of resources
• Self-recovery in protocol, using timeouts for lost or corrupted packets
Flow control, buffering and retries ensure isochrony and hardware buffer management
3.5.1 Error Handling
The protocol allows for error handling in hardware or software. Hardware error handling includes reporting and retry of failed transfers. A Wireless USB Host will try a transmission that encounters errors up to a limited number of times before informing the client software of the failure. The client software can recover in an implementation-specific way.
3.6 Security
All hosts and all devices must support Wireless USB security. The security mechanisms ensure that both hosts and devices are able to authenticate their communication partner (avoiding man-in-the-middle attacks), and that communications between host and device are private. The security mechanisms are based on AES 128/CCM encryption, providing integrity checking as well as encryption. Communications between host and device are encrypted using 'keys' that only the authenticated host and authenticated device possess.
3.7 System Configuration
Like wired USB, Wireless USB supports devices attaching to and detaching from the host at any time. Consequently, system software must accommodate dynamic changes in the physical bus topology.
3.7.1 Attachment of Wireless USB Devices
Unlike wired USB, Wireless USB devices 'attach' to a host by sending the host a message at a well defined time. The host and device then authenticate each other using their unique IDs and the appropriate security keys. After the host and device have been authenticated and authorized, the host assigns a unique USB address to the device and notifies host software about the attached device.
3.7.2 Removal of Wireless USB Devices
Devices can be detached explicitly by either the host or device using protocol mechanisms. Device detach also happens when a host is not able to communicate with a device for an extended period of time.
3.7.3 Bus Enumeration
Bus enumeration is the activity that identifies and assigns unique addresses to devices attached to a logical bus. Because Wireless USB allows devices to attach to or detach from the logical bus at any time, bus enumeration is an on-going activity for the USB System Software. Additionally, bus enumeration for Wireless USB also includes the detection and processing of removals.
4. DATA FLOW MODEL
4.1 Implementer Viewpoints
Wireless USB is very similar to USB 2.0 in that it provides communication services between a Wireless USB Host and attached Wireless USB Devices. The Wireless USB communication model view preserves the USB 2.0 layered architecture and basic components of the communication flow (i.e. point-to-point, same transfer types, etc
4.2 Communications Topology
The general communications topology of Wireless USB is identical to that used in USB 2.0 (see Figure 4-1). The obvious advantage of this is that many existing USB 2.0 functional components (in hosts and devices) continue to work without modification when the physical layer components supporting USB 2.0 are replaced with those supporting Wireless USB. The delta change from USB 2.0 to Wireless USB is illustrated to the right- hand side of Figure 4-1. The Function Layer is (almost) completely the same. The only difference is the isochronous transfer model has some enhancements to allow functions to react to the increased unreliability of the "Bus Layer". The Device Layer includes a small number of framework extensions to support security
and management commands required to manage devices on the wireless media. Finally, the Bus Layer includes significant changes to provide an efficient, secure communication service over a wireless media. The copper wire in USB 2.0 provides significant value with regards to security of data communications. The User knows which host the device is associated with because the device has to be physically plugged into a receptacle and the wire provides a specific path for data communications flow between a host and devices that cannot be casually observed by devices not purposely connected. Replacing the physical layer copper with a radio results in ambiguity about the actual association between devices and hosts, and also exposes data communication flows to all devices within listening range. In other words, the loss of the wire results in a significant loss of security which must be replaced by other mechanisms in order for Wireless USB to be a viable and usable technology. Wireless USB defines processes which allow a device and host to exchange the information required to establish a Secure Relationship (see Section 6.2.8). Alter a secure relationship has been established, the host and device have the necessary information required to support data encryption for "over the air" communications. Figure 4-1 illustrates how the standard USB data communications flow topology is extended for Wireless USB to include the concept of a secure relationship between a host and device and also illustrates that over-the-air data communications are encrypted. Notice that these new features extend only up to the device layer of the topology, allowing existing applications and device functions to exist and work without modification.
4.3 Physical Topology
Wireless USB Devices are not physically attached to a Wireless USB Host. Devices within radio range of a host establish a secure relationship with the host before application data communications are allowed. A host and its associated devices are referred to as a Wireless USB Cluster. A Wireless USB Cluster is comprised of a Wireless USB Host and all the Wireless USB Devices that it directly manages. Figure 4-2 illustrates an example physical topology enabled by Wireless USB. The host has a radio range of about 10 meters. Devices within the host's range can establish a secure relationship with the host and become part of the host's Wireless USB Cluster. All communication flows between the host and devices are point-to- point which means the physical topology of Wireless USB is a 1:1 match with the defined logical communications topology familiar to USB architecture. Likewise the client software-to-function relationship remains unchanged. Wireless USB also defines a specific class of device called the Wire Adapter that bridges between a Wireless USB bus and a USB 2.0 bus. The effect on the communications topology is essentially a cascading of USB busses.
5. POWER MANAGEMENT
Wireless USB provides mechanisms that allow hosts and devices to opportunistically and explicitly control their power consumption. Because Wireless USB protocol is TDMA-based, hosts and devices know exactly when their radios do not need to be transmitting or receiving and can take steps to conserve power during these times. Other mechanisms allow hosts and devices to turn off their radios for longer periods of time. The sections below cover power management mechanisms available for devices and for hosts and define the interactions between the two.
5.1 Device Power Management
Devices have three general ways to manage their Wireless USB power consumption. The first is to manage power during normal operation by taking advantage of the TDMA nature of Wireless USB protocol and opportunistically turning their radio off during periods when it isn't needed. Devices can do this at any time with the host being unaware of the efforts. The second way to manage power is to have the device go to 'sleep' for extended periods of time but still stay 'connected'. In this case the device will not be responsive to any communications from the host. Devices must notify the host before sleeping.
5.1.1Device Sleep
During periods of inactivity, a device may want to conserve power by turning off its radio and being unresponsive for an extended period of time. A device is required to notify the host before going to sleep and the host will acknowledge the notification.
5.1.2 Device Wakeup
After entering the Sleep state, devices may want to occasionally check with the host to find out if there is any work pending or the device may want to go back to the Awake state because the device now has data to deliver to the host (maybe for an Interrupt IN endpoint).
5.2 Host Power Management
A host has two general ways to manage Wireless USB power. The first can be done during normal operation by taking advantage of the TDMA nature of WUSB protocol and turning the radio off during periods when it is not needed. During times of low activity, the host can manage the Wireless USB channel to have long periods between MMCs(Micro-Sheduled Management Commands) and thereby have more time when the radio can be off. Devices are unaware of this power management, and since the Wireless USB channel is maintained, they just follow from one MMC to the next. The second general way for a host to manage power is to interrupt the Wireless USB channel, meaning that the continuous string of linked MMCs is stopped. Some typical reasons for the host to do this include:
The platform going to a low power state (Standby, Hibernate, ...)
The platform being shut down.
The user disabling the radio • Aggressive host power management For this case, devices are made aware of the hosts actions through an explicit, communication from the host.
6. PROTOCOL LAYER
This chapter presents a bottom-up view of the Wireless USB protocol starting at packet format definitions inherited from the MAC Layer standard and the application-defined extension required for Wireless USB.
6.1 Packet Formats
Wireless USB uses the packet (Frame) formats defined in the MAC Layer standard. The general structure of a packet is that it contains a PHY Preamble, PHY Header and MAC Header followed by a data payload (MAC frame body) which can be transmitted at a signaling rate different than that of the PHY and MAC Header (see top of Figure 6-1). The PHY layer provides standard support for error correction for all bits in the logical packet (PHY/MAC Header plus frame body). The PHY also CRC checks the PHY and MAC Header. The Frame Check Sequence field, which is the CRC value for the frame body payload is managed by the MAC layer. See the MAC Layer standard for implementation requirements. Note that when the Security bit component of the Frame Control field is set to zero (0), the security-related fields are not present in the packet. These fields are TKID, Rsrvd, Encryption Offset, SFN, and MIC. These fields are present if the Security bit is set to one (1).
7. SECURITY
This chapter provides Wireless USB security-related information. It describes the security inherent in wired USB (USB 2.0). This inherent security establishes a baseline that a wireless version must meet to be successful. When considering security solutions, one must keep in mind that no solution is currently or can be proven to be Impervious. Security systems are designed not to explicitly stop the attacker, but rather to make the cost of a successful attack far higher than any gain the attacker might realize from the attack. For the sake of brevity, when we say that a particular solution prevents attacks, we mean that the solution meets the objective listed above. The solution is not impervious, but the cost of compromising the solution outweighs the gain to be realized.
7.1 Encryption Methods
The standard method of encryption for the first generation of Wireless USB is AES-128 Counter with CBC- Mac (CCM). This is a symmetric encryption algorithm that uses the AES block cipher to create a robust stream cipher that can be used to provide integrity, encryption, or both. It is capable of real-time operation when Implemented in hardware. This is the only method currently defined for general session encryption.
Wireless USB also supports public key encryption, but only for authentication. Devices may choose to start a first-time authentication with public key encryption. In this case, PK encryption is used to authenticate the device and to protect the distribution of the initial CCM key. When PK is used, it will be used in a manner that will allow for software implementations of the algorithms.
The CCM encryption suite provides 128 bits of security for run-time operation. The PK cryptography suite must provide the same level of strength or else the strength of the entire suite is compromised. For this reason, Wireless USB will use RSA with 3072 bit keys for encryption and SHA-256 for hashing. The Security Architecture also recognizes a wired connection as an encryption method. This allows the SME to recognize a wired connection as a secure connection, without resorting to additional cryptography. This allows for wired/wireless devices, Where the wired connection can be used for initial CCM Connection Key distribution.
7.2 Message Format
Encryption will generally cause the message length to grow. In addition to the original message, the encrypted message must now contain additional keying material, freshness values, and an integrity value. The exact nature of these additional message components is dependent on the type of encryption used. In general, any new additional material added to the message, other than the integrity v|lue, will be added as a header. This header will immediately precede the encrypted message. The integrity value will immediately follow the message.
8. CONCLUSION
Wireless USB offers more band width than any other current wireless technology. Its power management and security features will enable it to wipe out all the current wireless personal interconnect. And tomorrow an office or a home computer will be cable free and inexpensive. Ease of installation and usage will makes Wireless USB the most accepted Wireless technology by the consumers.
9. FUTURE SCOPE
In future, every mobile phones, PDA's, Keyboard, Mice, Monitors, Projectors, External Storage, etc will become wireless. Today wireless USB is in the developing stage. In the middle of 2007 wireless USB will dominate the market.
Moreover, the scalable architecture of WUSB enable the technology to upgrade the data transfer rate more than 1 Gbps.
Many companies are now joining the WUSB special interest group and soon every product with a USB 2.0 connectivity will enable Wireless USB.
10. BIBLIOGRAPHY
1. www.usb.org
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