February 2003

HotSpot Backhaul Using Wireless High Speed Internet

BY ERIK BOCH

Recently, there has been a large focus on 802.11-based wireless technologies that enable a number of vertical markets including:

� The �hotspot� access market;

� Residential high speed access markets;

� Under-served SME markets; and

� Private emergency and disaster recovery back-up networks.

Using 802.11 technology, network operators are able to realize low cost, high-speed connectivity whilst not requiring licensing for each customer connection. Additionally, 802.11 technology offers some limited mobility to subtended data user terminals, potentially making it a candidate for integration into the mobile �3G� world. In addition to mobile/portable high-speed access applications, this technology also serves a range of other industrial and service industry needs.

802.11 technology also offers self-installed customer equipment functionality and can avoid costly outdoor antenna systems, making it highly attractive as the �next generation� high-speed residential access solution. The advent of 802.11a/g also enables the high speeds (54 Mbps inclusive of overheads) needed for this technology to have serious advantages over its wired competitors, namely:

� Wired 10BaseT LANs in the indoor environment;

� HFC and ADSL in the residential access environment;

� ADSL in the business access environment; and

� Wired 10BaseT Ethernet in the MAN (where it is available).

The numerous attractive attributes of 802.11 technology have made it a useful approach to solving various connectivity problems.

Indoor HotSpots

When 802.11 technologies are deployed indoors, a multiple base station solution is usually employed to attain the desired coverage solution within a typical office environment. It is well understood that in the indoor environment, longer range means lower speed. Therefore multiple base stations (access points) are generally connected into an aggregation device (LAN switch or router).

Typical examples of deployed indoor wireless networks are:

� Corporate LANs;

� LANs supporting computer portability/mobility in areas such as hospitals, hotels, airports, and shopping plazas; and

� Industrial and service sector LANs, such as various industrial and warehousing applications and reconfigurable restaurants and fast food outlets.

Outdoor HotSpots

The use of 802.11 technology is supported at 2.4 GHz and 5.8 GHz. The implementation of these hotspots typically differs somewhat from the indoor counterpart in that the access nodes tend to derive capacity by sectorization (rather than the method of increased node density which is typical of indoor scenarios). Sectorization also allows increased antenna gains that in turn allow larger access cell radiuses.

Bandwidth Demands of Individual HotSpots

802.11 technology used within the hotspot to connect the end-users is highly attractive due to the standard nature of the access devices and their low cost. 802.11 technology can be generally described as follows:

802.11b

� 2.4 GHz

� Currently being deployed

� ~ 6 Mbps shared Ethernet per access point (~ 11 Mbps with overheads included)
 

802.11g

� 2.4 GHz

� Currently being readied for deployment

� ~ 36 Mbps shared Ethernet per access point (~ 54 Mbps with overheads included)
 

802.11a

� 5.2 or 5.8 GHz

� Currently entering deployment

� ~ 36 Mbps shared Ethernet per access point (~ 54 Mbps with overheads included)

Modeling capacities in these cells is challenging due to the variety of end-user services that are possible and the unknown usage patterns of the users in this new �portable data� market. For instance, a business user may use 802.11 connectivity in the office and remain connected for the entire workday. The session is therefore very long in duration with very low average data rate. Activity is characterized to traffic that is largely constrained to the LAN, with some minor amounts of traffic going out of the LAN and into the Internet.

This same user, on travel, may log onto an out-of-office hotspot where the session may be a quick download of a day�s worth of e-mail. In this case, the session is short but at very high bandwidth. All of the data in this case is to/from the Internet. Inadvertently, this user also places new stresses on the host corporate Internet connection since it is now required to upload the user�s e-mail load, a task that it normally did not have to accomplish with any great speed previously since the mail was either served locally or loaded into the Internet towards a requesting remote user on dial-up (or other �low speed� out-of-office connection).

As an example of the hotspot traffic that might be expected, several typical types of hotspots can be modeled using first-order estimates of the access usage in the cell. Backhauling the data from these cells can be accomplished through a number of means, either wireline or wireless.

Aggregation Bandwidths

In a given region, a service provider may be supporting numerous hotspots, which deliver a given service or services to end customers. Aggregation of these cells can be accomplished through several wireless network architectures, namely:

� Organic addition of HotSpots using intercell linking and point-to-point (PTP) Ethernet �add-dropping.�

� HotSpots can be connected using Multi-Point (MPT) wireless aggregation cells.

The �add-drop� aggregation allows the operator to add infrastructure onto the network at a rate, which is roughly compatible with revenue growth achieved through the added HotSpot cells. The Intercell links can easily run into the 50�200 Mbps and beyond capacities when considering the aggregation of a few HotSpots. Additionally, the links ideally need to be remotely �up-speedable� so that the service provider does not need to pay for maximum envisioned bandwidths at the outset but has the capability to up-speed individual intercell link segments to cope with the organic growth of the network.

The intercell connections that are suspended between each of the hotspot clusters will form the backbone structure for the service. This is not unlike the architecture adopted by the mobile service industry in which the network was rapidly built-out using a completely wireless solution. The aggregation backboning will require that both secure and reliable technology be used, taking an asset-based approach with secure licensed point-to-point spectrum for this critical backhaul requirement.

The Multipoint links to the HotSpots can be added as the HotSpots are set into service. The Multipoint node is generally a multi-sectored structure with a minimum entry configuration. The availability of 5.8 GHz unlicensed spectrum or licensed spectrum at 3.5 GHz is ideally suited for this Multipoint aggregation layer, assuming that individual HotSpots are low bandwidth. The aggregation node is then backhauled into the network metro core using high speed Point-to-Point technology. As discussed previously, this Point-to-Point layer is obviously implemented using licensed radio technology so that interference immunity is ensured. This immunity translates into reliable, predictable operation, and secure revenue generation.

SUMMARY

HotSpot deployments are undergoing high growth and often employ wireless technologies to address backhauling and HotSpot interconnections. A variety of network topologies and wireless technologies can be employed to realize these functions. Both Licensed and unlicensed wireless technologies fulfill critical roles in the various network topologies. Unlicensed technology is well suited for the end-user access layer(s) whilst licensed technologies are clearly better suited for the higher speed aggregation and backhauling layers. The use of High speed Ethernet in the backhaul allows for highly scaleable/�up-speedable� links with low cost �add-drop� functionality.

Erik Boch is chief technology officer for DragonWave, Inc. DragonWave designs, markets and supports broadband, wireless networking products for service providers and enterprises requiring reliable, predictable, interference-free, high-bandwidth transmission of real-time, IP applications. DragonWave is headquartered in Ottawa, Canada�s high-technology capital. The company�s Web site is www.dragonwaveinc.com.

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