Next-generation wireless network standard technology HiperLAN/2

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Next-generation wireless network standard technology HiperLAN/2 [Copy link]

Because wireless networks are not limited by physical lines, they have advantages that wired networks cannot match. In response to the needs of wireless LAN applications, various manufacturers have launched a series of wireless LAN (WLAN) products based on the 802.11 standard, which provide bandwidths ranging from 1Mbps to 11Mbps. However, the performance of these wireless network products is far from comparable to that of traditional fixed network products, which makes it seem that there is no substantial difference in performance between today's wireless networks and wide-area cellular networks using technologies such as GSM and AMPS. Although some data communications with lower rates (about 10kbps) are also supported, the main application of these wireless networks is to support voice services. In order to meet the needs of future Internet/Intranet access, the industry is developing a new generation of WLAN and cellular network technologies, which will improve QoS (in order to create a multi-service network), security and performance.

This article introduces the next generation wireless LAN technology (WLAN) called HiperLAN/2 developed by the HiperLAN/Global Forum (H2GF). H2GF was initiated by companies such as BoschTelcom, Dell, Ericsson, Nokia, TeliaMobile and TexasInstruments, and its purpose is to promote the standardization of HiperLAN/2 technology. The most striking feature of HiperLAN/2 is that it can operate in the 5GHz frequency band, while traditional wireless LAN technologies mostly use the 2.4GHz frequency band of the 802.11 standard. The HiperLAN/2 standard was finalized at the end of last year.

Network structure and function

The topology of a HiperLAN/2 network is shown. The mobile terminal (MT) communicates with the access point (AP) through a wireless interface determined by the HiperLAN/2 standard. MT users can move freely in the HiperLAN/2 network, and HiperLAN/2 can ensure that users and MTs get the best transmission performance. A MT only communicates with one AP at a time. No matter where the user moves, the HiperLAN/2 wireless network can detect the AP that can provide the best performance for the MT at each moment and automatically establish a connection with the AP. It is reported that two MTs can also communicate directly without a wireless interface, but this technology is still in the research and development stage, and the specific details have not yet been disclosed.

HiperLAN/2 defines detection functions and conversion signaling to support many wireless network functions, including dynamic frequency selection (DFS), link adaptation, wireless cell switching, multi-beam antennas and power control.

Dynamic Frequency Selection

This feature allows several network providers to share available spectrum and can be used to avoid mutual interference between frequencies. Each AP performs frequency selection through filtering interference measurements performed by the AP and its associated MTs.

Link Adaptation

In order to meet the needs of various wireless transmission service quality, HiperLAN/2 uses a link adaptation scheme in terms of signal-to-interference ratio (C/I). The range of C/I varies according to the location where the HiperLAN/2 system is deployed, and C/I can vary according to the communication conditions in the surrounding wireless cells. The link adaptation scheme measures the degree to which it adapts to the physical layer based on the quality of the link. Therefore, the network can dynamically select SCH (short transmission channel) and LCH (long transmission channel) for each transmitted MAC frame.

antenna

HiperLAN/2 supports multi-beam antennas, which can increase the C/I ratio of the wireless network and improve the performance of the wireless network. The MAC protocol and frame structure in HiperLAN/2 allow the use of 7-beam antennas.

Conversion

The switching scheme is initiated by the MT, that is, each MT performs necessary detection of the surrounding APs and selects the most suitable AP for communication. The switching detection method is not defined in the HiperLAN/2 standard, so some manufacturers switch based on signal strength, and some manufacturers switch based on other quality standards. The HiperLAN/2 standard defines the necessary signaling to complete this switching.

Power Control

HiperLAN/2 supports transmitter power control in both MT (uplink) and AP (downlink). MT power control is mainly used to simplify the design of AP receivers. AP power control is part of the HiperLAN/2 standard.

How it works

A HiperLAN/2 scheme with one MT and three APs supporting Q tags with priority indication (Q?tag) is shown.

In HiperLAN/2, each AP uses the DFS algorithm to select a suitable frequency. First, the MT will detect the signal strength and select the most appropriate AP to establish contact with it. The MT receives a MAC number (MAC ID) from the selected AP, and then exchanges link functions and decides what authentication process and encryption algorithm to use, as well as which aggregation layer to use for user communication. After key exchange and authentication, the MT and AP can establish contact. Finally, a user connection is established at the data link control layer (DLC), and the user can communicate at this time.

MT will send and receive data through two established connections (the default value in HiperLAN is 2), which support two different priority queues with Q tag mapping (of course, more priority queues can also be supported). The Ethernet aggregation layer ensures that the priority of each Ethernet frame is mapped to the appropriate data link layer user connection according to the pre-defined mapping scheme.

MT can decide to join one or more multicast groups. HiperLAN/2 network can be configured to use N unicasts to get the best transmission quality, or assign a separate MAC number (MAC ID) to each joined group to reserve bandwidth for it. If a single MAC number is assigned to a multicast group, the mapping scheme is: IP address - IEEE address - MAC number.

When the MT moves, if it detects that there is an AP that is more suitable for communication (such as having better signal strength), it will perform a switch. All established connections will be automatically switched to the new AP through the fixed LAN using AP-AP signaling. When the MT (or more precisely, the user) wants to disconnect from the LAN, the MT will request to disconnect, thus disconnecting all connections between the MT and the AP. When the MT moves beyond the coverage of HiperLAN/2, all connections between the MT and the AP will also be disconnected.

Main Features

The main features of HiperLAN/2 technology include the following aspects:

High transfer rate

HiperLAN/2 has a very high transmission rate. Its physical layer transmission rate can reach up to 54Mbps, and the third layer transmission rate can reach up to 25Mbps. In order to achieve such a high rate, HiperLAN/2 uses a modulation method called Orthogonal Frequency Digital Multiplexing (OFDM) to transmit analog signals. OFDM is very effective in time-dispersed environments (such as offices), where wireless signals transmitted may be reflected by many points, causing them to have different propagation times before they finally reach the receiver. At the physical layer, HiperLAN/2 uses a new media control layer (MAC) protocol, which uses a dynamic time division duplexing technology to make the most efficient use of wireless resources.

Connection-Oriented

Traditional wireless networks are all connectionless. In a HiperLAN/2 network, you need to use the signaling function of the HiperLAN/2 control board to establish a connection between the MT and the AP before data can be transmitted. The connection is established using the wireless interface time division multiplexing technology. There are two types of connections used in HiperLAN/2, namely point-to-point connections and point-to-multipoint connections. Point-to-point connections are bidirectional, while point-to-multipoint connections are unidirectional, that is, they only point to the mobile terminal MT. In addition, there is a dedicated broadcast channel for transmitting data from an AP to all terminal MTs.

QoS Support

The connection-oriented nature of HiperLAN/2 makes it easy to meet QoS requirements. A specified QoS can be assigned to each connection to determine the connection's requirements in terms of bandwidth, delay, congestion, bit error rate, etc. In HiperLAN/2, it is also possible to use a simpler method, that is, each connection can be assigned a different priority tag. This QoS support, together with the high transmission rate, ensures that different data sequences (such as video, voice, and data, etc.) can be transmitted at high speed at the same time.

Automatic Frequency Assignment

In HiperLAN/2 networks, there is no need to manually plan frequencies as in cellular networks (such as GSM). The wireless base station (called access point AP in HiperLAN/2) itself supports the selection of the most appropriate wireless channel for each AP's transmission within its coverage area. (Continued from page D26) Each AP monitors neighboring APs and other wireless resources in the HiperLAN/2 environment, and selects the most appropriate transmission channel based on the two principles of whether the wireless channel is already occupied by other APs and minimizing interference to the wireless network environment.

Security Support

HiperLAN/2 supports authentication and encryption. By using the authentication mechanism, AP and MT can authenticate each other to ensure authorized access to the network (from the AP's perspective) or to ensure access to a valid network provider (from the MT's perspective). The authentication mechanism in HiperLAN/2 relies on some other supporting functions (such as directory services, etc.), but these supporting functions themselves are not included in the HiperLAN/2 technology.

When users communicate over an established connection, encryption can be used to prevent real-time eavesdropping and man-in-the-middle attacks.

Mobility support

MT will be able to automatically transmit and receive data from the nearest AP. More precisely, the wireless signal provided by the AP used by MT has the best signal-to-noise ratio. Therefore, when the user and MT move, MT may detect that there is another AP with better wireless transmission performance than the AP currently in use. At this time, MT will automatically switch to this AP. All previously established connections will be transferred to this new AP, so that MT is still on the HiperLAN/2 network, so there will be no interruption in communication. However, some packet loss may occur during the conversion.

If a MT is out of the coverage of the wireless HiperLAN/2 for a period of time, the MT may disconnect from the HiperLAN/2 network, which will release all existing connections.

Network and application independence

The HiperLAN/2 protocol stack has a flexible structure, so it is easy to adapt and integrate with a variety of fixed networks. For example, a HiperLAN/2 network can be used as the last segment of a switched Ethernet, but it may also be used in other configurations, such as as an access network to a third-generation cellular network. All applications that can run in fixed networks today can run in HiperLAN/2 networks.

Low power consumption

In HiperLAN/2, the MT power saving mechanism is based on the sleep state initiated by the MT. The MT can request the AP to enter a low-power sleep state at any time, and can determine the duration of this state. When the negotiated sleep period expires, the MT searches for a wake-up indication from the AP. If no wake-up indication is found, the MT will switch back to a low-power state and enter the next sleep period. During the sleep period, the AP will delay all waiting data transmission tasks until the corresponding sleep period in the MT ends. HiperLAN/2 supports different sleep times, which can meet users' different needs for short delays or low power.

Application Areas

HiperLAN/2 has a wide range of applications. The following are some of the most typical applications.

Enterprise LAN

It shows an enterprise network built using Ethernet LAN and IP routers. In this network, a HiperLAN/2 network is used as the last segment between MT and LAN. HiperLAN/2 network supports mobility within the same LAN/subnet. Moving between subnets means IP mobility.

Important Locations

HiperLAN/2 can be deployed in key locations (such as airports, hotels, etc.) to provide remote access and Internet services to users who are traveling. Access servers connected to HiperLAN/2 allow point-to-point connections and access to specific corporate networks (which may require access through a specific ISP).

Access to third generation cellular networks

Users can access third-generation cellular networks (such as WCDMA, etc.) through HiperLAN/2. In the future, the areas covered by HiperLAN/2 and WCDMA technologies will become increasingly extensive, and users can get the most benefit from them. They can not only use the services provided by HiperLAN/2, but also use WCDMA cellular network services in places without HiperLAN/2. When users move between the two types of networks, the core network can ensure that users switch between the two types of networks seamlessly and automatically.

Home Network

HiperLAN can create a wireless infrastructure for the home environment, used for networking home devices (such as home PCs, VCRs, cameras, and printers). HiperLAN/2's high output and QoS features can meet the requirements of video transmission and data communication for various home devices. In this case, the AP may provide an "uplink" link to the public Internet.