White paper MIMO in the Metro

Radio Frequency Engineering Connecting Asia’s world cities Commuters on These days most commuters like to utilise reach into these confined spaces, dedicated One network, many challenges Engineering (RFE), the network is founded on The result is shared network infrastructure MTR’s new West Island Line the time they spend either waiting for or infrastructure needs to be deployed to Modern confined coverage infrastructure is a multi-band 2G, 3G and 4G (800-2700MHz) supporting 2G, 3G and 4G services for riding upon public transport. Once limited to propagate the signal within. typically founded on broadband distributed DAS featuring multiple input multiple output all four of Hong Kong’s mobile carriers – can enjoy uninterrupted newspaper broadsheets or paperback books, (MIMO) long term evolution (LTE) technology spanning CDMA (850MHz), GSM (900MHz Hong Kong MTR Corporation (MTR) has antenna systems (DAS) – comprising either wireless data at speeds of the options for making every minute count to markedly boost capacity and alleviate data and 1800MHz), WCDMA (850 MHz, 900MHz long recognised this and has been a global a network of indoor antennas or radiating continue to escalate in the 21st century with traffic congestion. and 2100MHz), FD-LTE (1800MHz and up to 600Mbps – thanks to pioneer since the first confined coverage cables (leaky feeders) to deliver contoured the functionality and speed of smart phones 2600MHz) and TD-LTE (2300MHz). With the MIMO and one of the world’s communications system for passengers coverage within a space. Some form of signal and tablets. The drive for higher capacity incorporation of LTE MIMO, the overall system was deployed in 1993. Now, with the recent amplification is usually required to cover most advanced confined Capacity, as much as coverage itself, is is capable of delivering combined ultra-high Whether it’s catching up on business emails, opening of the city’s new West Island Line, a larger spaces and distances – for example, of critical importance in mobile network cellular data throughputs of over 5Gbps. coverage networks, designed online entertainment, social media or simply three-station and 3km extension of the MTR’s the signal may be transmitted over optical design – particularly in environments like the and delivered by Radio the news of the day, commuters increasingly Island Line, the MTR is once again leading fibre to an optical repeater, which feeds a The multi-band wireless coverage extends Hong Kong MTR, which experiences mass expect uninterrupted wireless data access the way. passive DAS. to all areas associated with three new Frequency Engineering (RFE), congregations of people with the time and along the whole of their journey – including A key feature of such systems is their underground stations – (SYP), a BAI Communications (BAI) inclination to use digital devices. Hong Kong’s in underground stations and subway tunnels. broadband nature – they are typically University (HKU) and (KET) – population is not only one of the most densely company based in Hong Kong. Since outdoor cellular networks cannot designed to support the services of all along with approximately 3km of dual-bore distributed, but also one of the most data- commercial carriers, and often additional tunnels. The station areas covered include hungry, prompting the drive for new, higher- private radio and public safety services as the entrance gates to each station, concourse capacity 4G technologies such as MIMO. well. As the number of RF services increases and station platforms, and passenger lifts and new bands are utilized, the network MIMO is a method for effectively doubling the at HKU and SYP stations – all designed to design challenges just keep multiplying – capacity of 4G LTE networks by using multiple give commuters a seamless wireless data especially as user demand and expectation antennas for both transmit and receive at experience. escalate. the same time. Hong Kong’s premier telecom services provider, HKT, which operates the Hong Kong’s West Island Line thus opened in city’s leading mobile carrier, CSL, drove the December 2014 with what is believed to be incorporation of LTE MIMO into the West one of the world’s most advanced confined- Island Line network, by means of carrier * Data throughput of up to 600Mbps only available to space wireless coverage solutions. Designed users with compatible LTE-ACat6 handsets. aggregation technology, to offer data speeds and delivered by Radio Frequency of up to 600Mbps per user*. Architecture and a half As a regional leader in the tailored design and entrances, elevators, and so on as required, The interference equation To minimise the introduction of passive The main challenge with MIMO in general is integration of confined coverage systems, with each sector covering the full 800-2700 To manage interference in this complicated intermodulation (PIM), the system utilises the much higher likelihood of interference RFE was appointed to design and deliver the MHz. The highest capacity network is HKU system, RFE carefully calculated the signal the highest-performance equipment BILLION occurring within the system, owing to solution. The resulting network architecture is station, with six sectors deployed. levels for all sectors that would result in (including antennas, cables, repeaters, filters 1.6 HONG KONG SUBWAY PASSENGERS substantially more complex than previously and connectors). This also demanded that transmitting and receiving simultaneously on The broadband RF distribution system minimum interference without affecting PROVIDED WITH CONNECTIVITY EACH YEAR deployed networks, requiring the highest installation crews deliver the highest-possible the same cable and antenna network. This for each sector is either a radiating cable users. The network was then designed to quality standards in engineering design workmanship. During installation, each of demands sophisticated network engineering (tunnels) or indoor antenna network; many deliver those precise signal levels, with high- and installation to manage interference and thousands of connections was rigorously to minimise interference, even for carriers’ of these also incorporate fibre networks with performance filters added to all sub-bands. MBPS outdoor networks, which can be physically maintain the strongest signal quality levels to tested to ensure it met the PIM design 600 multi-band optical repeaters An additional design challenge involved the DATA SERVICE EXPERIENCED BY separated from each other. In the multi-band achieve the data rate. specifications. Installation and commissioning positioning of antennas to exploit multipath COMMUTERS IN HONG KONG’S MTR to achieve the required signal levels. The took a period of three months, and included West Island Line confined coverage network, Each of the three new stations has a MIMO-compatible optical repeaters used propagation, which is used to control which supports all carriers’ services on the extensive testing of system performance centralised point of interconnection to provide interference in MIMO systems. This is easier in the West Island Line architecture were inside a running train. same network (a total of 20 sub-bands interfaces for the base stations of each specially designed to meet the high capacity when antennas are spaced far apart, as in spanning 800-2700MHz), the interference commercial mobile service in Hong Kong. The and power requirements of the system – as outdoor networks, a luxury not available in challenges associated with MIMO become signals from these base stations are combined well as the high number of sub-bands. The confined spaces. In tunnel systems, which significantly multiplied. and distributed via up to six sectors – tunnel entire system can support a traffic capacity of incorporate radiating cables instead of point #1, tunnel #2, concourse, platforms, long antennas, this is even more of a challenge. London Toronto Data whenever they want Boston New York Hong Kong

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Anecdotal feedback from commuters Indeed, it is undoubtedly one of the highest- Only those behind the scenes – in particular suggests they welcome the quality of capacity tunnel coverage networks in the RFE and Hong Kong’s commercial carriers, mobile data services along the West Island world; not only does it support MIMO LTE for which identified the demand – will ever baicommunications.com | [email protected] Line – from both a coverage and capacity those with the most advanced handsets, but is appreciate the high level of engineering perspective. compatible with all 2G, 3G and 4G commercial required to get the network up and running. services in Hong Kong, spanning 20 sub- All commuters will experience is seamless bands from 800-2700MHz. This is one of the data connectivity and the ability to check their highest number of services supported by a phones and tablets whenever they want. single broadband network.