HIPERLAN - the approaching standard for Wireless LAN's

by
Torben Rune, Netplan A/S
September 3. 1997.

Index

Why use radio-based Local Area Networks?

Todays typical LAN environment require costly planning and investment to build and maintain. Radio-based LANs might soon become a more flexible and even less expensive option in dynamic environments, than todays cable based systems.

As production facilities grow more and more based on information technology, having a local area network becomes increasingly crucial to ensuring things like teamwork, workflow and decision support and even for practical purposes like backup of enterprise data and important IT-based production tools.

As enterprises grow, their needs for office space or larger production facilities rise. At the same time, the enterprises knowledge of the direction or scale of the coming growth might be limited. In such an environment, small companies may find it very hard to pick the right time when the company is able to absorb the high cost of establishing or expanding a cable-based LAN.

Figure 1- A simple radio based LAN configuration

The emergence of radio based LAN communications products is set to offer enterprises the option of building their LANs on more flexible and maybe even cheaper wireless technology. With wireless technology, businesses might also reduce the total planning costs (where to put cables and where their pc’s, printers and so on).

Wireless technology will also make it less demanding to move computer equipment to new locations, that lack easy access to LAN cables.

Other possible applications of wireless technology in general are in public institutions that currently have little or no infrastructure. Microsoft Corporation stated in a discussion "that a wireless broadband network is potentially the only economically practical means of disseminating multimedia data within a classroom."

Emerging wireless technologies share some of the potentials and challenges of other technologies where the end-user products are in the process of being miniaturized. The potential is, that miniaturization can lead to replacing today’s bulky equipment with more transportable equipment that are generically portable. While this may lead to rising usability of Wireless products for consumers, it also raises the challenges of honoring a number of technical and regulatory requirements. Just to mention a small obstacle, international and national telecommunications authorities require that official stickers be placed directly on the product to show the consumer, that the product has been tested and approved. As the products get smaller, the challenge of finding space for such stickers becomes greater.

The Wireless technology is still in its infancy. Existing wireless equipment manufacturers only offer proprietary products. In fact, the technology is today primarily known and used for military and exotic purposes.

One of the biggest barriers to the growth and diffusion of this technology is the lack of standardization. The lack of current standards raises the risk for business consumers wishing to take advantage of this exciting technology. They might find, that the products of today might not be able to work with the standards of tomorrow.

A recent survey shows that the most widespread use for wireless technology today is for E-mail, leased-line replacement, internet access and wired LAN replacement (each used by 1/3 of users polled). At the same time only very few use wireless technology for vertical market (transportation, insurance sales, etc) and disaster recovery. Just under half of the users polled state, that they have introduced wireless technology in order to reduce line costs, while just over half in another question state that the cost of wireless is keeping them from investing in the technology.

Once standards are adopted, economics of scale set in and businesses slowly adapt to wireless LAN technology, new exiting products and applications will surely emerge.

The need for standardization of wireless communication

The need for bandwidth in LAN based communication equipment has been constantly rising. New user-friendly technology such as graphics based documents and program- interfaces have strained many existing LAN infrastructures and the emergence of real time high definition video transmissions are sure to strain these infrastructures further.

A new standard for wireless communication also had to address these challenges. The new technology had to be not only exciting but also able to meet tomorrow’s needs for bandwidth. For example, the emerging standard on compressed progressive digital video (MPEG3) currently requires individual data streams of 18 Mb pr. Second. This cannot be accommodated in any commercially available wireless equipment.

With the need for bandwidth in wireless communications also come the need to address the problems of quality of the transmission service. Especially video signals are very prone to drastic reductions of quality once the bandwidth drops even if only momentarily. Once the bandwidth drops, the video frame can freeze and the sound and the video signals might loose its synchronization.

The need for secure communications

One problem facing wireless communication is the perception that wireless communication can easily be eavesdropped by others. Fortunately, a number of initiatives have sought to ensure that using wireless communications become secure and not unwillful broadcasting services.

The European ETS 300 328 standard stipulates that frequency spreading must be used. Frequency spreading is a technique in which the communications equipment is configured to use several frequencies to communicate, thereby making it impossible to eavesdrop by listening in on a single frequency.

The spreading techniques normally used in wireless LAN products can be divided into two families: Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS). The first approach resists interference by jumping rapidly from frequency to frequency in a pseudorandom way. The receiving system has the same pseudorandom algorithm as the sender, and jumps simultaneously. The second approach resists interference by mixing in a series of pseudorandom bits with the actual data. The receiver, using the same pseudorandom algorithms, strips out the extra bits.

In a spread spectrum system, there is a possibility to multiplex users by assigning them different spreading keys. Such a system is called a Code Division Multiple Access (CDMA) system. However, most wireless LAN products are not CDMA systems since users belonging to the same wireless LAN utilize the same spreading key. Instead users are multiplexed in time using nearly the same Carrier Sense Multiple Access (CSMA) protocol as in the Ethernet.

Global standardization efforts

One of the major problems concerning this technology is standardization. The problems concerning standardization are among other things making the best use of a scarce resource - the radio spectrum while at the same time making the standard attractive enough to use so the market can grow.

A number of global and national standardization initiatives have taken place in wireless technology.

The global organization IEEE has been working 6 years on the 802.11 standard, which is almost ready to be adopted. The 802.11 standard accommodates both infra-red and spread-spectrum radio with a protocol CSMA/CA (carrier-sense multiple access/collision avoidance) similar to CSMA/CD used in the Ethernet.

In the US a new standard called NII/SUPERnet has been introduced concerning wireless communications in the 5,150-5,350GHz and 5,725- 5,875GHz band.

JAPAN has introduced the SPDCS standard ("Small Power Data Communication System), which operates at 2,4Ghz. JAPAN has also introduced standards in the 19Ghz spectrum - Light Wireless Communications System (LWCS) and in the 30-300GHz spectrum - Millimeter Wave Wireless LAN (MWWL).

Europe has introduced the Digital European Cordless Telecommunications (DECT) standard (which is not a LAN standard) and has just introduced the HIPERLAN standard after several years of work.)".

The networking industry itself has taken an important initiative under the name of WLANA, (members are 3Com, Aironet Wireless Communications, AMD, Digital, Harris Semiconductor, IBM, Lucent Technologies, Norand, Proxim, Raytheon Electronics, Symbol Technologies, Windata and Xircom). WLANA promises 'to promote increased awareness and knowledge of wireless LANs among potential customers, independent software vendors and systems integrators'.

What is HIPERLAN?

HIPERLAN is a European family of standards on digital high speed wireless communication in the 5,15-5,3Ghz and the 17.1-17.3Ghz spectrum developed by ETSI. The committee responsible for HIPERLAN is RES-10 which has been working on the standard since November 1991.

The standard serves to ensure the possible interoperability of different manufacturers' wireless communications equipment that operate in this spectrum. The HIPERLAN standard only describes a common air interface including the physical layer for wireless communications equipment, while leaving decisions on higher level configurations and functions open to the equipment manufacturers.

The choice of frequencies allocated to HIPERLAN was part of the 5-5,30GHz band being allocated globally to aviation purposes. The Aviation industry only used the 5-5,15GHz frequency, thus making the 5,15-5,30 frequency band accessible to HIPERLAN standards.

HIPERLAN is designed to work without any infrastructure. Two stations may exchange data directly, without any interaction from a wired (or radio-based) infrastructure. The simplest HIPERLAN thus consists of two stations. Further, if two HIPERLAN stations are not in radio contact with each other, they may use a third station (i.e. the third station must relay messages between the two communicating stations).

Products compliant to the HIPERLAN 5 Ghz standard shall be possible to implement on a PCMCIA Type III card. Thus the standard will enable users to truly take computing power on the road.

The HIPERLAN standard has been developed at the same time as the development of the SUPERnet standard in the United States.

HIPERLAN requirements

  • Short range - 50m
  • Low mobility - 1.4m/s
  • Networks with and without infrastructure
  • Support isochronous traffic
  • audio 32kbps, 10ns latency
  • video 2Mbps, 100ns latency
  • Support asynchronous traffic
  • data 10Mbps, immediate access

Quality of service

Performance is one of the most important factors when dealing with wireless LANs. In contrast to other radio-based systems, data traffic on a local area network has a randomized bursty nature, which may cause serious problems with respect to throughput.

Many factors have to be taken into consideration, when quality of service is to be measured. Among these are:

  • The topography of the landscape in general
  • Elevations in the landscape that might cause shadows, where connectivity is unstable or impossible.
  • Environments with many signal-reflection surfaces
  • Environments with many signal-absorbing surfaces
  • Quality of the wireless equipment
  • Placement of the wireless equipment
  • Number of stations
  • Proximity to installations that generate electronic noise
  • and many more

The sheer number of factors to take into consideration means, that the physical environment will always be a factor in trying to asses the usefulness of using a wireless technology like HIPERLAN.

Simulations show that the HIPERLAN MAC can simultaneously support

  • 25 audio links at 32kbit/s, 10ms delivery
  • 25 audio links at 16kbit/s, 20ms delivery
  • 1 video link at 2Mbit/s, 100ms delivery
  • Asynch file transfer at 13.4Mbit/s

Benchmarking HIPERLAN in practise

Once a new HIPERLAN installation is implemented, trying to benchmark it can easily become a mind-boggling task.

Even though a spectrum analyzer can be used for initial evaluation and troubleshooting, the factors influencing performance are so many and so complex, that initial benchmarking should be based evenly on perceived performance and registered performance over a longer period of time.

In contrast to cable based LANs, the testing equipment has to find the communication stream in the air not on a physical cable and it has to monitor several frequencies at once. On top of that, the testing equipment itself can interfere with the signals it intends to monitor.

New HIPERLAN standards ahead

A new set of standards are under construction for a new version of HIPERLAN - HIPERLAN2. The idea of HIPERLAN2 is to be compatible with ATM.

There is also undergoing work to establish global sharing rules. The WINForum for NII/SUPERNET in the US aim to support HIPERLAN 1 and HIPERLAN 2. This effort involves interaction between ETSI RES10, WINForum, ATM Forum.

Figure 2 - The future of HIPERLAN

HIPERLAN-related projects

HIPERION aims to create and demonstrate a European capability for high-performance radio networking for portable computers.

One of the reasons for the establishment of HIPERION is in their own words "Portable computers will play an ever increasingly important role in business, education and leisure environments in coming years. Communications technologies which permit access to information and services as well as those which enable collaboration and sharing will be fundamental technologies for tomorrow's information based economies."

Standards

ETS 300 836-(1-4) (ed.1)

Radio Equipment and Systems (RES);
HIgh PErformance Radio Local Area Network (HIPERLAN);
Type 1 Conformance Testing Specification;
Part 1: Radio Type Approval and Radio Frequency (RF) - Conformance Test Specification

Part 2: Protocol Implementation Conformance Statement (PICS) - performance specification

Part 3: Test Suite Structure and Test Purposes (TSS&TP) specification

Part 4: Abstract Test Suite (ATS) specification

RES10

sPE: 14-02-1997

ETS 300 652 (Ed.1)

Radio Equipment and Systems (RES); HIgh PErformance Radio Local Area Network (HIPERLAN) Type 1; Functional specification

CEPT Recommendation T/R 22-06 permits the operation of high speed radio local area networks in the 5,15 to 5,30 GHz and 17,1 to 17,3 GHz frequency bands. These types of radio networks are referred to as HIgh PErformance Radio Local Area Networks (HIPERLANs).

This ETS specifies the technical characteristics of HIPERLAN Type 1 that operates in the 5,15 to 5,3 GHz frequency band and that uses Non-Pre-emptive Priority Multiple Access (NPMA) as the channel access method.

HIPERLAN Type 1 is confined to the lowest two layers of the Open Systems Interconnection (OSI) model: the Physical Layer and the Medium Access Control (MAC) part of the Data Link Layer. Functions of higher layers are required for operation and interworking of a complete systems. These higher layers are outside the scope of this document.

This ETS does not address the requirements and technical characteristics required for type approval and conformance testing. These are covered in a separate HIPERLAN ETS.

Separate ETSI standards address other types of HIPERLAN systems.

Reference
Read Netplan's background article on wireless LANs from 1995.

BIOGRAPHY
Torben Rune received his Masters degree in computer technology from the Technical University of Denmark, Copenhagen in 1983. In 1989 he formed his own company, and has since that worked as an independent consultant in the field of tele- and datacommunications and managing director of Netplan Aps. During 1992 as an ETSI member, Torben Rune held the position as team leader of PT41, the project team under RES-10 responsible for defining the coming ETSI Hiperlan standard. Contact by internet e-mail tr@netplan.dk. Netplan has a home-page at: http://www.netplan.dk.