2.6 GHz Spectrum & the Next Generation Mobile Broadband Networks



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As the much awaited 2010 Mobile world Congress will kick in on 15th February in Barcelona, Spain, primary focus will be on discussing and showcasing the future of mobile broadband industry with cutting edge products, technologies highlighting m-commerce, m-marketing, m-advertisements, broadband deployment and initiatives broadening the mobile ecosystems.

“There is clear evidence that the volume of data flowing over mobile networks is growing rapidly and is being accelerated by the popularity of smart phones and the growth in music and video downloads,” said Tom Phillips, Chief Regulatory Affairs Officer at the GSMA.

With this unique and new view of the mobile landscape unfolding, one of the primary driver will be the utilization of ever scarce resource: Spectrum. The licensing of the 2.6 GHz spectrum will be vital in satisfying the demand for greater capacity for Mobile Broadband and launching next-generation networks such as LTE, which will start to be deployed commercially around the world this year .

As I mentioned in my previous article covering the WiMAX business model highlighting the importance of the spectrum and its contribution in the wireless operator’s cost model. Building on it we now know that the licensing of the 2.6 GHz band will be critical to unlocking the benefits of global scale economies in the Mobile Broadband market. The outcome of 2.6GHz allocation will have far-reaching consequences for how the adoption dynamics of WiMAX and 3GPP (such as HSPA and, in future, LTE) will play out in this region since 2.6GHz is the first arena where the two proponents will be battling each other in the same area of spectrum.

So let’s jump in discussing and analyzing about the 2.6GHz band its importance, what’s in store and bullet its implications on the future of mobile broadband. This analysis extends the scope of the report on 2.6 GHz band recently released by the GSMA & GVP. This report maybe biased towards LTE but lets draw some real pointers and analyze it.

Digging in about 2.6GHz band..

The 2.6 GHz band (2500-2690 MHz), sometimes also referred as the 2.5 GHz band, was allocated by the World Radio communication Conference (WRC) in 2000 for terrestrial mobile communications services. The 2.6GHz band is often referred to as the “IMT-2000 expansion band”(now !!) or the “3G expansion band”(earlier) and is 190MHz wide (substantial !!). This band has been allocated on primary basis to all the three ITU regions for terrestrial mobile communications compared to the smaller allocation of 3.5 GHz (3.4-4.2 GHz) Why ??

Note: ITU Regions: Region 1 comprises Europe, Africa, the Middle East west of the Persian Gulf including Iraq, the former Soviet Union and Mongolia; Region 2 covers the Americas, Greenland and some of the eastern Pacific Islands; Region 3 contains most of non-former-Soviet-Union Asia, east of and including Iran, and most of Oceania.

WRC imposed stringent power limits on satellite systems with limited geographic footprint operating in 2.6 GHz band shifting the importance of satellite systems more into 3.5 GHz bands. Also to add to this WRC-07 decided against the global identification for IMT, including WiMAX, in any part of the satellite C band (3.4-4.2 GHz)  with an exception of the mobile service allocation in 3.4-3.5 GHz thus making this band less globally harmonized for IMT. Hence the 2.6GHz band is now in a unique position to be exploited as a common band for commercial terrestrial mobile broadband access services on a global basis.

The beauty of the 190MHz wide spectrum is how it is to be divided for allocation. Should it be paired or unpaired suiting to corresponding FDD and TDD modes of operations.

The International Telecommunications Union (ITU) presents three possible options:

Option I: A mix of FDD(paired) and TDD(unpaired) spectrum plan which avoids interference problems this two different modes of operations

Option II: No unpaired spectrum included in this plan and leaves the second member of each pair undetermined

Option III: A Flexible plan on the amount of spectrum allocation for either of the paired(FDD) or unpaired(TDD) modes of the operation

The adoption of above plans differs from region to region, country to country and market to market depending upon the  technology Standard to be deployed either HSPA/HSPA+, LTE or WiMAX. A channel width of 20 MHz is recommended for most efficient use of current technology capabilities  for FDD (2×20 MHz) as well as TDD (a 20 MHz block is sufficient). Licensing should be based on a structure of 5 MHz channel blocks to allow support for 5,10, 15 or 20 MHz channels dependent on spectrum availability and each market’s competitive situation. Future technology evolution (4G) will most likely be based on combining multiple channels with 20 MHz being an ideal building block.

The ITU Option 1 band plan is well suited to meeting this goal by enabling technology neutrality and competitive ―4G‖wireless equipment choices for both FDD and TDD operation to mobile operators (including both LTE and WiMAX).There is widespread agreement at national levels as well as at the European Union and its Commission in adoption of Option 1 band plan.

Recent licensing carries a bias toward Option 1 with slight differences related to country-specific situations. More auctions are expected in Europe as well as in major emerging markets such as Brazil and South Africa. Substantial 2.6 GHz spectrum is licensed in the United States, although allocation and utilization are less than ideal for unique, nonreproducible historical reasons that predate the allocation of this band to mobile communications.

The ITU Option 2 band plan does not accommodate demand for unpaired spectrum and, therefore, violates the principle of technology neutrality (WiMAX)

The ITU Option 3 might lead to is likely to lead to multiple different national band plans and other challenges such as regulatory hurdles coupled with interference management and costs and availability of the equipment to match up in a customized way to the different national band plans. It increases the need for guard bands and could drive costs up for spectrum owners since they would need to negotiate with each other to make sure efficient coexistence and sacrifice spectrum to use as guard bands

2.6 GHz Spectrum implications:

Socio – Economic Implications

• Expanding the wireless mobile broadband to developed as well as developing nations  at affordable price points

• With a standardized spectrum bands and allocations plan allowing global harmonization will help drive economies of scale driving the costs down

• Standardization also enables easy and ready accessibility of the common services across many geographies.
• Economic reuse and sharing of existing physical and operational infrastructure  of the mobile operators reducing CAPEX (deployment costs)

• Proper Spectrum standardization and band plans options enables technology (FDD/TDD) and service neutralities  facilitating innovation and healthy competition between equipment, device, and applications and services vendors to the benefit of customers

• The widespread mobile broadband deployment and growth have potential benefits (employment, GDP) for developed economies and in fact more for emerging economies.

Technological Implications

• LTE and WiMAX can exploit 20 MHz of contiguous spectrum to deliver their highest spectral efficiency and highest throughputs. The 2.6 GHz band makes such allocation possible enabling the operators to operate high-speed LTE/WiMAX services at optimum performance.
• The 2.6 GHz frequencies have relatively short propagation ranges and inferior in-building penetration characteristics compared to lower frequencies makes it less suitable for rural areas( But with beam forming this can be taken care of..)
• On the other hand, the short propagation range and the large amounts of bandwidth (190 MHz) available in this band make it ideal for operators seeking to offer high network capacity and improve the speeds of mobile data transmission they can deliver to users in urban and suburban areas.
• Looking ahead, the shorter 2.6 GHz wavelengths can achieve greater improvements in performance through increased use and capabilities of smart antenna techniques such as MIMO and beam forming than is possible at lower frequencies. Thus, the gaps between environments in which 2.6 GHz can be used economically and efficiently relative to those where frequencies below 1 GHz are better suited may be somewhat reduced in favor of 2.6 GHz.
• The 2.6 GHz spectrum is the ideal complement to the 700 MHz spectrum, also known as ‘digital dividend’, and will enable the most cost-effective nationwide coverage of Mobile Broadband across both rural and urban environments. Also, LTE is likely to be of interest in other bands (e.g. 1800 MHz in Finland and Hong Kong).
• Though I mentioned at the start 2.6 GHz was seen as the “3G Extension band” but the ITU has changed its destination to the IMT band (for all mobile applications) positioning it strong for growth of 4G technologies (LTE Advanced & 802.16m).

2.6 GHz Adoption Facts:

• Recent licensing of this band in Hong Kong, Norway, Finland and Sweden, for example, has highlighted that there is more demand for paired (FDD) than unpaired spectrum (TDD) and that the ITU’s recommended Option 1 plan is the best structure to stimulate market growth in a technology-neutral and competitive environment. With an

• In the United States band plan, incumbents have the flexibility to deploy Time Division Duplex (TDD) or Frequency Division Duplex (FDD) anywhere in the band (Option 3) . Here the major spectrum owners are Sprint & Clearwire deploying TDD WiMAX which will be followed by future LTE rollouts by Verizon Wireless possibly in 700MHz band and AT&T is currently focusing on HSPA/HSPA+ networks to match up to WiMAX speeds.

• Governments in most Western European countries as well as in Brazil, Chile, Colombia, and South Africa are planning to award 2.6 GHz frequencies within the next two years.

Summarizing the benefits, implications, facts and the mobile broadband trends, 2.6 GHz spectrum ownership and band allocation can shape the business models for the next generation technologies. It will be a significant part in developing a wireless ecosystem which will offer high-speed mobile broadband solutions which shall  be easy to access, seamless across geographies and at an affordable price !!

- Neil Shah

References:

Unstrung.com Report : 2.6GHz Spectrum Key for LTE
Maravedis-bwa.com : Europe Prepares for 2.6 GHz spectrum Feeding Frenzy
Five bidders take 2.6 GHz WiMAX spectrum in Norway
GSMA & GVP Report on "The 2.6 GHz Spectrum Band"
WiMAX Forum 2.5 GHz Spectrum Manager
Light Reading : GSMA Wants More LTE Spectrum
3G Americas: LTE Global Deployments
WiMAX Vision.com4G battle looms in Europe at 2.6GHz

Femtocells & Relays in Advanced Wireless Networks

With the huge growth of mobile phones complementing with a revolution wireless network technologies there has been a huge change in the consumer’s lifestyle and dependence on mobile phones. With the emergence of smart phones (mobile web) consumers are replacing not only their fixed lines but have started downsizing the number of personal computers in home. But they have far way to go as this demographic for this adoption is quite limited due to various factors. Fundamentally, consumers want great voice quality, reliable service, and low prices. But today’s mobile phone networks often provide poor indoor coverage and expensive per-minute pricing. In fact, with the continued progress in broadband VoIP offerings such as Vonage and Skype, wireless operators are at a serious disadvantage in the home.

Hence the wireless operators are looking to enhance their macro-cell coverage with the help of micro-cell coverages(indoor) deploying small base stations such as Femtocells or with the help of Relay technology.These miniature base stations are the size of a DSL router or cable modem and provide indoor wireless coverage to mobile phones using existing broadband Internet connections.

Pointing out some key advantages of Femtocells and Relays we will then focus on their adoption in advanced wireless networks(WiMAX and LTE)

FEMTOCELLS

Technical Advantages:

Low Cost: The Business Model would be initially by offering Femtos as a consumer purchase through mobile operators

Low Power: around 8mW- 120 mW lower than Wi-Fi APs.

Easy to Use: Plug-and-Play easily installed by consumers themselves

Compatibility & Interoperability: Compatibility with UMTS,EVDO standards and WiMAX,UMB & LTE standards

Deployment: In Wireless Operator owned licensed spectrum unlike WiFi

Broadband ocnnected:Femto cells utilize Internet protocol (IP) and flat base station architectures, and will connect to mobile operator networks via a wired broadband Internet service such as DSL, cable, or fiber optics.

With the above set up Femtocells solves following existing problems and extends the wireless coverage reach enabling newer applications and services

Customer’s point of view:

Increased Indoor Coverage: Coverage radius is 40m – 600m in most homes providing full signal throughout the household

Load sharing: Unlike in macro cells which supports hundreds of users, Femtos will support 5-7 users simultaneously  enabling lesser contention in accessing medium delivering higher data rates/user.

Better Voice Quality: As the users will be in the coverage envelope and closer to Femtos, they will definitely be supported with a better voice and sound quality with fewer dropped calls

Better Data/Multimedia Experience: It will deliver better and higher data performance with streaming musics, downloads and web browsing with lesser interruptions and loss of connections compared to a macro-cell  environment

Wireless Operator’s point of view:

Lower CAPEX: Increased usage of femtocells will cut down huge capital costs on macro cell equipments & deployments. This includes costs savings in site acquisitions, site equipments, site connections with the switching centers.

Increased network capacity: Increased usage of femtocells will reduce stress on macro cells increasing overall capacity of mobile operators

Lower OPEX: With lesser macro cell sites it reduces the overall site maintenance, equipment maintenance and backhaul costs.

Newer Revenue Opportunities: With provision of excellent indoor coverage and superior user experience with voice and multimedia data services operators has an opportunity of raising its ARPU with more additions to family plans

Reduced Churn: Due to improved coverage, user multimedia experience and fewer dropped calls, will lead to a significant reduction in customer churn

Technical hurdles:

Spectrum: Femtocells works on licensed spectrum and as the spectrum is the most expensive resource it will be a major technical hurdle for the wireless operator for frequency planning.

RF Coverage Optimization: Radio tuning and optimization for RF coverage in macro cells is manually done by technicians which is now not possible at each femtocell level, henceforth self optimization and tuning over time according to the indoor coverage map has to be done either automatically or remotely which is a technical challenge.

RF Interference: Femtocells might be prone to femto-macro interference and also femto-femto interference in highly dense macro or micro environments which might affect the user experience.

Automatic System Selection: When an authorized user of a femto cell moves in or out of the coverage of the femto cell – and is not on an active call – the handset must correctly select the system to operate on. In particular, when a user moves from the macro cell into femto cell coverage, the handset must automatically select the femto cell, and visa versa

Handoffs: When an authorized user of a femto cell moves in or out of coverage of the femto cell – and is on an active call – the handset must correctly hand off between the macro cell and femto cell networks. Such handoffs are especially critical when a user loses the coverage of a network that is currently serving it, as in the case of a user leaving the house where a femto cell is located

Security & Scalability: A femto cell must identify and authenticate itself to the operator’s network as being valid. With millions of femto cells deployed in a network, operators will require large scale security gateways at the edge of their core networks to handle millions of femto cell-originated IPsec tunnels

Femto Management: Activation on purchase and plug and play by end user is an important step and with a proper access control management allowing end-user to add/delete active device connections in the household. In addition, operators must have management systems that give first-level support technicians full visibility into the operation of the femto cell and its surrounding RF environment.

RELAYS:

Relay transmission can be seen as a kind of collaborative communications, in which a relay station (RS) helps to forward user information from neighboring user equipment (UE)/mobile station (MS) to a local eNode-B (eNB)/base station (BS). In doing this, an RS can effectively extend the signal and service coverage of an eNB and enhance the overall throughput performance of a wireless communication system. The performance of relay transmissions is greatly affected by the collaborative strategy, which includes the selection of relay types and relay partners (i.e., to decide when, how, and with whom to collaborate).

Relays that receive and retransmit the signals between base stations and mobiles can be used to effectively  increase throughput extend coverage of cellular networks. Infrastucture relays do not need wired connection to network thereby offering savings in operators’ backhaul costs. Mobile relays can be used to build local area networks between mobile users under the umbrella of the wide area cellular networks

Advantages:

Increased Coverage: With multi-hop relays the macro cell coverage can be expanded to the places where the base station cannot reach.

Increased Capacity: It creates hotspot solutions with reduced interference to increase the overall capacity of the system

Lower CAPEX & OPEX: Relays extending the coverage eliminates the need of additional base stations and corresponding backhaul lines saving wireless operators deployment costs and corresponding maintenance costs. The relays can be user owned relays provided by operators and can be mounted on roof tops or indoors.

Better Broadband Experience: Higher data rates are therefore now available as users are close to the mini RF access point

Reduced Transmission power: With Relays deployed there is a considerable reduction in transmission power reducing co-channel interference and increased capacity

Faster Network rollout: The deployment of relays is simple and quickens the network rollout process with a higher level of outdoor to indoor service and leading to use of macrodiversity increasing coverage quality with lesser fading and stronger signal levels

As a hot research topic with great application potential, relay technologies have been actively studied and considered in the standardization process of next-generation mobile communication systems, such as 3GPP LTE-Advanced

and IEEE 802.16j (multihop relays for WiMAX standards).

Relay Types

Two types of RSs have been defined in 3GPP LTE-Advanced and 802.16j standards, Type-I and Type-II in  3GPP LTE-Advanced, and non-transparency and transparency in IEEE 802.16j.

Specifically, a Type-I (or non-transparency) RS can help a remote UE unit, which is located far away from an eNB (or

a BS), to access the eNB. So a Type-I RS needs to transmit the common reference signal and the control information for the eNB, and its main objective is to extend signal and service coverage.Type-I RSs mainly perform IP packet forwarding in the network layer (layer 3) and can make some contributions to the overall system capacity by enabling communication services and data transmissions for remote UE units.

On the other hand, a Type-II (or transparency) RS can help a local UE unit, which is located within the coverage of an eNB (or a BS) and has a direct communication link with the eNB, to improve its service quality and link capacity. So a Type-II RS does not transmit the common reference signal or the control information, and its main objective is to increase the overall system capacity by achieving multipath diversity and transmission gains for local UE units.

Pairing Schemes for Relay Selection

One of the key challenges is to select and pair nearby RSs and UE units to achieve the relay/cooperative gain. The selection of relay partners (i.e., with whom to collaborate) is a key element for the success of the overall collaborative strategy. Practically, it is very important to develop effective pairing schemes to select appropriate RSs and UE units to collaborate in relay transmissions, thus improving throughput and coverage performance for future relay-enabled mobile communication networks.

This pairing procedure can be executed in either a centralized or distributed manner. In a centralized pairing scheme, an eNB will serve as a control node to collect the required channel and location information from all the RSs and UE units in its vicinity, and then make pairing decisions for all of them. On the contrary, in a distributed pairing scheme, each RS selects an appropriate UE unit in its neighborhood by using local channel information and a contention-based medium access control (MAC) mechanism. Generally speaking, centralized schemes require more signaling overhead, but can achieve better performance

Relay Transmission Schemes

Many relay transmission schemes have been proposed to establish two-hop communication between an eNB and a UE unit through an RS

Amplify and Forward — An RS receives the signal from the eNB (or UE) at the first phase. It amplifies this received signal and forwards it to the UE (or eNB) at the second phase. This Amplify and Forward (AF) scheme is very simple and has very short delay, but it also amplifies noise.

Selective Decode and Forward — An RS decodes (channel decoding) the received signal from the eNB (UE) at the first phase. If the decoded data is correct using cyclic redundancy check (CRC), the RS will perform channel coding and forward the new signal to the UE (eNB) at the second phase. This DCF scheme can effectively avoid error propagation through the RS, but the processing delay is quite long.

Demodulation and Forward — An RS demodulates the received signal from the eNB (UE) and makes a hard decision at the first phase (without decoding the received signal). It modulates and forwards the new signal to the UE (eNB) at the second phase. This Demodulation and Forward (DMF) scheme has the advantages of simple operation and low processing delay, but it cannot avoid error propagation due to the hard decisions made at the symbol level in phase one.

Comparison between 3GPP LTE Advanced and IEEE 802.16j RSs

Below shows comparison between Type I(3GPP- LTE Advanced) and Non-Transparency(IEEE -802.16j) RSs

Technical Issues

Practical issues of cooperative schemes like signaling between relays and different propagation delays due to different locations of relays are  often overlooked.  If  the difference in time of arrival between the direct path from source to destination and the paths source-relay-destination is constrained then relays must locate inside the ellipsoid as depicted below. Thus,  in practice, such a cooperative system shoiuld be a narrow band one, or guard interval between transmitted symbols should be used to avoid intersymbol interference due to relays.

In band relays consume radio resources and Out of band relays need multiple transceivers.

References:

IEEE P802.16j/D9, “Draft Amendment to IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems: Multihop Relay Specification,” Feb. 2009.

S. W. Peters and R. W. Heath Jr., “The Future of WiMAX: Multihop Relaying with IEEE 802.16j,” IEEE Commun.Mag., vol. 47, no. 1, Jan. 2009, pp. 104–11.

Y.Yang, H. Hiu, J. Xu, G. Mao, “Relay technologies for WiMAX and Advanced Mobile systems” IEEE Commun. Mag., Oct,2009.

C. K. Lo, R. W. Heath, and S. Vishwanath, “Hybrid-ARQ in Multihop Networks with Opportunistic Relay Selection,” Proc. IEEE ICASSP ‘07, Apr. 2007, pp. 617–20.

HSPA, EVDO, WiMax then LTE but what about the mobile backhaul??

With HSPA, EVDO maturing, WiMax getting deployed and LTE getting ready to buzz around, it is soon changing the way mobile phones will access the networks. The bandwidth hungry new services, applications and the non-stop touch clicks on your smart handhelds are eventually going to obsolete these mature 3G networks. Whereas, the 4G access networks are definitely envisioned to control this ever-increasing wireless broadband traffic but what bout the evolution of backhaul?? Is it ready? or is it going to be a major bottleneck analogous to the traffic jams seen if only one lane was operating out of a four lane expressway.

So, let’s have a closer look on how the mobile backhaul network is currently positioned.

The trend below depicts the exponential growth in asynchronous data demand for next 5 years.

Mobile Traffic Projections for the next 5 years

Over the next few years, “user experience” will still continue to rely on 3G (and in some regions on 2G) technology.But for the mobile operator, LTE/WiMax is already part of the game plan. Operators have to learn the technology, and its impact on their networks, applications and service offering. Though, service providers are seeking revenue and profit growth through new differentiated packet-based services. Many of these services, such as mobile Internet and mobile TV, require high bandwidth—and the current backhaul infrastructure is not optimized for handling such traffic. Hence, providers have to add backhaul capacity while keeping operational costs under control, a situation that is forcing carriers to migrate their access and core networks to the new 3G and 4G infrastructure.

There are three main transport technologies in the backhaul arena – fiber, copper and wireless point-to-point microwave.

The costs of backhaul form a significant part of service providers’ revenue accounting for three quarters of mobile transport costs and 25-30% of total operating expenses. The 2G infrastructure carried voice traffic through switched TDM (T1/E1 or SDH/SONET) or ATM. As with 3G/4G services, already  the bandwidth requirements have shot exponentially and to transport voice and data efficiently has been the need of the hour.

Basic requirements for a 4G Backhaul network:

1. Capacity: A single tail site should be scalable to 100Mbps+ capacities to avoid bottlenecks

2. Latency: A solution that supports 10msec or less end-to-end latency

3. All IP: Support IP traffic from head to tail.

Current migrating strategy is transporting Ethernet packets over point-to-point Microwave. Over 50% of all mobile backhaul deployments worldwide (and nearly 70% outside the U.S.A.), point-to-point microwave systems offer simple and cost efficient backhauling for voice and high-speed data services. That’s because point-to-point microwave supports higher data rates than traditional copper T1/E1 lines, it delivers between 25% and 60% more bits compared with similar TDM based systems, and easily overcomes the high cost and limited availability associated with fiber. Thus, operators can connect the TDM ports today, and gradually shift traffic to the Ethernet ports in the future. This shift can be done from remote, so no additional CAPEX or OPEX are needed. The industry has already established that the end game of next generation mobile backhaul networks is all-IP/Ethernet. Ethernet is not only more scalable, it also offers huge cost savings across the entire network value chain.

Ethernet cost savings per 1 Million subscribers

Also migrating to high capacity and lower latency Ethernet/All IP network, the systems should also support QoS aware Adaptive Coding and Modulation and Statistical Multiplexing. The former helps optimizing network for spectrum efficiency, increasing the radio capacity and  thus reducing cost/bit and latter in optimizing traffic management over the network reducing congestion and improving efficiency. An IP over Ethernet infrastructure has the advantage of the bandwidth growth curve of Ethernet moving from 10 Megabits per second (Mbps) to 10 Gigabits per second (Gbps) today and 100 Gbps in future. This coupled with the decreasing cost of Ethernet ports provides growth opportunities with increasing economies of scale.

Ethernet microwave Vs. TDM microwave equipment cost comparison

Thus, of the three backhaul technology options operators can choose from, wireless point-to-point microwave can deliver the best cost-performance features, bringing faster ROI and driving forward the proliferation of advanced mobile services in the LTE/WiMax era. But in the longer run a hybrid  solution of microwave, optical or IP/MPLS core might be seen as a balanced solution that might reduce the OPEX with improved scalability, higher bandwidth, lower latency and better efficiency. So operators pull up the socks and get ready for the great migration.

Also, a point to note with CISCO’s recent acquisition of Starnet Networks which makes it now one of the most dominant player in mobile backhaul solutions market.

From the recent news releases:

Verizon has committed to deploying fiber to 90% of the cell sites in its territory by 2013, closely following VZW’s LTE rollout schedule

Qwest plans to run fiber 7,500 to 17,000 cell sites in its territory

- Neil Shah

References:

“ATM to ALL IP”  Cost effective Network Convergence – Tellabs ’2009.

“LTE Backhaul Solutions”- Ceragon June 2009

Cable Backhaul: A towering OpportunityWebinar Harris Stratex Networks Nov’2009