Broadband Wireless Local Loop Trial Report Version: 5.1 Date: 1 December 2003

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Broadband Wireless Local Loop Trial Report

Broadband Wireless Local Loop Trial Report Version: 5.1 Date: 1 December 2003

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TABLE OF CONTENTS

1 EXECUTIVE SUMMARY...............................................................................................3

2 INTRODUCTION.............................................................................................................5 2.1 BASIC ISP INFRASTRUCTURE.........................................................................................6 2.2 WCDMA-TDD TECHNOLOGY......................................................................................7 2.3 TRIAL OBJECTIVES ........................................................................................................8

3 TRIAL CONFIGURATION ............................................................................................9 3.1 CELL SITES LOCATION...................................................................................................9 3.2 NETWORK CONFIGURATION ........................................................................................10 3.3 RADIO AIR INTERFACE CONFIGURATION.....................................................................10

4 TRIAL RESULTS...........................................................................................................11

4.1 RADIO COVERAGE AND PERFORMANCE ANALYSIS......................................................11 4.2 CHANGE OF UL/DL RATIO BY TIMESLOT ASSIGNMENT................................................13 4.3 INTERNET PLATFORM INTEGRATION TEST...................................................................13

4.3.1 Tier of service ......................................................................................................13 4.3.2 Subscriber Authentication....................................................................................14

5 CONCLUSIONS..............................................................................................................15

Broadband Wireless Local Loop Trial Report Version: 5.1 Date: 1 December 2003

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1 EXECUTIVE SUMMARY

As one of Asia's leading integrated communication companies, PCCW always invests and delivers innovative services that enhance the lifestyles and businesses of our customers. Recognizing the important role of broadband technologies in Hong Kong's information infrastructure, PCCW conducted a field study of emerging broadband fixed wireless access (FWA) or wireless local loop (WLL) technology with permission from OFTA. Most fixed broadband WLL equipment vendors have chosen either Code Division Multiple Access (CDMA) or Orthogonal Frequency Division Multiplexing (OFDM) as the basis of their new point-to-multipoint products. Reasons usually cited for the selection include capability of the technology to support high rate multimedia services, efficient use of spectrum, ability to support a large number of users, and robustness to multipath. Both OFDM and CDMA are the foundations of many wireless systems and products, so both are well-researched and known to the wireless community at large. The trial system has implemented Time Division Duplex - CDMA (TDD-CDMA) and other advanced techniques to deliver theoretical maximum 3Mbps downlink data rate in an unpaired 5MHz spectrum, depending on radio propagation conditions and sharing among users located inside one sector of a cell site. The dense urban environment of Hong Kong is always a good place to verify the practical performance and limit of new radio technologies and networks. Overall the TDD-CDMA system performed well, delivering on average more than 2Mbps of aggregated data rates close to 3Mbps at strong signal location to outdoor users and close to 1 Mbps to indoor users under normal interference conditions. The system employs rate adaptation to deliver the optimum data rate to the user. If the user was in very poor radio coverage conditions the throughput fell to less than 200kbps rather than having no service at all. The TDD-CDMA system proved to be reliable in the coverage area. It has also demonstrated that WCDMA technology enables good NLOS characteristic which is a significant advantage over LMDS technology. The NLOS property will greatly improve service provision and avoid the need for installation of external antenna for users in many cases. With frequency reuse of N=1, the amount of interference from other base stations will cause the greatest impact to throughput because they all operate in the same frequency. Careful site planning must be used to mitigate the most serious cases and avoid significant network performance degradation. The planning is similar to a CDMA system in terms of interference mitigation. In conclusion, the new WCDMA based broadband WLL system has solved many deficiencies of LMDS and MMDS systems. The adoption of TDD requires only a single unpaired frequency band giving more flexibility in spectrum management. The

Broadband Wireless Local Loop Trial Report Version: 5.1 Date: 1 December 2003

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ratio of uplink and downlink data rates can be asymmetrical and adjusted to meet the service requirement. In contrast, Frequency Division Duplex (FDD) cannot reassign unused uplink capacity to downlink. With this trial, we hope to demonstrate that there are viable broadband wireless technologies in addition to 3G and 802.11 wireless LAN. A flexible and supportive spectrum management policy will help the adoption of these innovative technologies thus maintaining Hong Kong's position as the leading wireless Internet metropolitan region.

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2 INTRODUCTION

PCCW is one of Asia’s leading integrated communication companies. PCCW provides a spectrum of communications services from local telephony to broadband services to business solutions and more. PCCW always invests and delivers innovative services that enhance the lifestyles and businesses of our customers; keeping Hong Kong ahead with the most advanced telecommunications infrastructure. Although penetration of broadband in Hong Kong is relatively high, there are still locations that are out of reach of wireline broadband service or the network upgrade cost is too high to justify. In parallel, there are a growing number of broadband users connecting 802.11b wireless LAN devices to their broadband lines. There are a number of reasons for this, but mainly for the convenience of moving around inside the home. This leads to the belief that broadband WLL can still play a role in Hong Kong broadband infrastructure. Despite the lack of success of LMDS in Hong Kong, the new generation WLL systems show many improvements over their predecessor. Traditionally, WLL systems require a clear line of sight from the customer’s building to the service provider’s base station. They have to be aligned with stringent precision and the service quality for those high frequency systems may degrade due to weather conditions, especially heavy rainfall. The latest WLL technology does not require line of sight, or outdoor installation. The user terminal enables “zero-installation” and can be placed anywhere inside the home. These systems usually operate at less than 3.5GHz and based on a number of modulation technologies such as OFDM, CDMA or TDD-WCDMA. To assess the true performance of new generation WLL in Hong Kong’s unique environment, PCCW conducted a field trial of a TDD-WCDMA WLL system. The trial was run from November 2002 to April 2003. Two radio stations were setup in Wanchai district; covering roughly one third of the area. The radio stations were connected to the ISP infrastructure to offer broadband Internet service.

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2.1 Basic ISP Infrastructure One criterion in assessing the new WLL technology is the ease of integrating it seamlessly with the existing ADSL broadband infrastructures and the delivery of the same basic services as ADSL.

ADSL Network

WLL Network

Internet

RADIUSServer

ISP Platform

Border Router

Access Router Backbone

Switch

DSLAM

RadioBase Station

LDAPServer

Figure 1 - Integration with existing ISP infrastructure

As indicated in Figure 1, an ISP infrastructure based on ADSL technology usually consists of the following basic elements:

Platform element Basic function Access Router

Provide a termination point for end users’ IP traffic

Backbone Switch

Connecting different routers and servers

RADIUS server

Provide user authentication and accounting function

LDAP server

Store user profiles (username, password, class of service, etc.)

Border router

Connect the ISP platform to the Internet

DSLAM ADSL equipment

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2.2 WCDMA-TDD Technology WCDMA is a wideband Direct-Sequence Code Division Multiple Access (DS-CDMA) system. User information bits are spread over a wide bandwidth by multiplying the user data with quasi-random bits (called chips) derived from CDMA spreading codes. The TDD (Time Division Duplex) uses the same frequency band but alternates the transmission direction in the time (Figure 1).

Uplink Timeslots

Downlink Timeslots

Switching Point between Up- and Downlink

Principle of TDD Operation

Time

Power DensityFrequency

5MHz

Figure 2 - Principle of TDD operation

TDD operates in the unpaired spectrum using a single frequency channel for both uplink and downlink traffic. This is done by switching between transmission directions with proper control of switching transients. To avoid corrupted transmission, the uplink and downlink transmissions require a common means of agreeing on transmission direction and allowed time to transmit. This is achieved in the test system by using GPS as a timing reference. Corruption of transmission is avoided by allocating a guard period which allows uncorrupted propagation to counter the propagation delay. Another benefit introduced by TDD is asymmetric uplink/downlink capacity allocation. In TDD operation, uplink and downlink are divided in the time domain. It is possible to change the duplex switching point and move capacity from uplink to downlink, or vice versa, depending on the capacity required between uplink and downlink. This

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capability fits the asymmetric nature Internet traffic where download traffic 10 times of upload traffic making TDD a suitable candidate for data applications.

2.3 Trial Objectives

• To assess the general performance of new WLL technology in Hong Kong environment.

• To verify that the new WLL system can seamlessly integrate with existing ISP infrastructure and provide similar basic functions. (i.e. QoS, authentication and accounting, etc.)

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3 TRIAL CONFIGURATION

3.1 Cell Sites Location The field trial was arranged in the Wanchai district because of its dense urban environment which was typical in Hong Kong and represented the worst case scenario for evaluating any wireless technology. Two base stations were installed and codenamed LKT and TMH respectively. These locations offered a good representation of a typical Hong Kong environment. The core network equipment was installed in a nearby exchange.

Figure 3 - Trial site locations

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3.2 Network Configuration The trial system was composed of the following: • Antenna • Radio Base Station • Access Router • Backbone Switch • Wireless Modem

Both site locations were connected to the access router at the exchange via fiber connections, reusing the existing ISP ADSL platform.

Internet

ISP Router

Base-station

Base-stationWirelessModem

Antenna

Desktop PC

Antenna

RADIUSServer

ISP Platform

Access Router

BackboneSwitch

LDAPServer

WLL

Figure 4 - Trial configuration

3.3 Radio Air Interface Configuration The system employs TDD and the uplink/downlink are transported over the same RF channel. In the test system, there are 15 slots per frame with frame duration of 10ms.

Time slot 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Function Signaling Signaling Downlink Downlink Downlink Downlink Downlink Downlink Downlink Downlink Downlink Signaling Uplink Uplink Uplink

Direction ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↑ ↑ ↑ ↑

Table 1 - Timeslot configuration

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4 TRIAL RESULTS

4.1 Radio Coverage and Performance Analysis The purpose was to identify the size of outdoor and indoor coverage and throughput.

Table 2 - Throughput and map legend

--

~200kbps>400kbps>800kbpsIndoor rate

- ~200kbps>400kbps>800kbps>1Mbps

Outdoor

No serviceMarginal

Map Indoor cvgOutdoor

No service

Fair Good Excellent

No service

Marginal Fair Good

Figure 5 - TMH coverage plot

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Figure 6 - LKT coverage plot

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4.2 Change of UL/DL ratio by timeslot assignment The result indicates that the ratio of downlink and uplink traffic can be adjusted via different timeslot assignment.

No. of uplink time slots

No. of downlink time slots

Ideal ratio of uplink to downlink data rates

Actual ratio of uplink to downlink data rates

2 10 1 : 5 1 : 5.23 3 9 1 : 3 1 : 3.38 6 6 1 : 1 1 : 1.33

4.3 Internet Platform Integration Test

4.3.1 Tier of service ADSL service offers different tier of data rates and this test was to assess the ability of the WLL system to limit the user data rate according to different service plans.

Class-of-service

In this test, Class of service weighting enforced a distribution of throughputs among the users according to the weighting defined by the service operator.

100%

77%

26%

51%

75%

100%

25%

50%

0%

20%

40%

60%

80%

100%

120%

Biz Gold Silver Bronze

Group

Wei

ght

Resulted Distribution

Target Setting

Figure 7 – Class-of-service weighting distribution

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Rate Limiting The objective was to verify that the user could not achieve a greater average throughput than the service plan allowed.

100%

60%

35%

87%75%

25%

50%

100%

0%

20%

40%

60%

80%

100%

120%

Biz Gold Silver BronzeGroup

Wei

ght

Resulted Distribution

Target Setting

Figure 8 – Rate limiting weighting distribution

4.3.2 Subscriber Authentication In the trial, a PPPoE client software was installed in the user’s computer performing similar as ASDL PPPoE dialer. A user logged to the network by authenticating the Username/Password. Result: The system integrated seamlessly with the existing Radius authentication platform and rejected calls with an invalid username or password.

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5 CONCLUSIONS

Overall the TDD-CDMA system performed well, delivering on average more than 2Mbps of aggregated data rates close to 3Mbps at strong signal location to outdoor users and close to 1 Mbps to indoor users under normal interference conditions. The system employs rate adaptation to deliver the optimum data rate to the user. If the user was in very poor radio coverage conditions the throughput fell to less than 200kbps rather than having no service at all. The TDD-CDMA system proved to be reliable in the coverage area. It has also demonstrated that WCDMA technology enables good NLOS characteristic which is a significant advantage over LMDS technology. The NLOS property will greatly improve service provision and avoid the need for installation of external antenna for users in many cases. With frequency reuse of N=1, the amount of interference from other base stations will cause the greatest impact to throughput because they all operate in the same frequency. Careful site planning must be used to mitigate the most serious cases and avoid significant network performance degradation. The planning is similar to a CDMA system in terms of interference mitigation. In this trail with a 5MHz spectrum bandwidth, it was observed that the performance of WCDMA TDD technology at the cell edge was not stable. This has affected the overall system performance and cell size. It is believed that if the spectrum bandwidth doubles to 10MHz, there would be improvement on the cell edge’s performance. Study on how these changes applied to the urban environment in HK will be valuable In conclusion, the new WCDMA based broadband WLL system has solved many deficiencies of LMDS and MMDS systems. The adoption of TDD requires only a single unpaired frequency band giving more flexibility in spectrum management. The ratio of uplink and downlink data rates can be asymmetrical and adjusted to meet the service requirement. In contrast, Frequency Division Duplex (FDD) cannot reassign unused uplink capacity to downlink.