Thursday, 28 June 2007

OFDM and OFDMA: The Difference

I was curious as to why IEEE 802.16d (fixed service) uses Orthogonal Frequency Division Multiplexing (OFDM). IEEE 802.16e (mobile) uses Orthogonal Frequency Division Multiple Access (OFDMA). So, what’s the difference between the two, and why is there a difference?

Lets first look at FDM:

In FDM system, signals from multiple transmitters are transmitted simultaneously (at the same time slot) over multiple frequencies. Each frequency range (sub-carrier) is modulated separately by different data stream and a spacing (guard band) is placed between sub-carriers to avoid signal overlap.

OFDM is sometimes referred to as discrete multi-tone modulation because, instead of a single carrier being modulated, a large number of evenly spaced subcarriers are modulated using some m-ary of QAM. This is a spread-spectrum technique that increases the efficiency of data communications by increasing data throughput because there are more carriers to modulate. In addition, problems with multi-path signal cancellation and spectral interference are greatly reduced by selectively modulating the “clear” carriers or ignoring carriers with high bit-rate errors.
Like FDM, OFDM also uses multiple sub-carriers but the sub-carriers are closely spaced to each other without causing interference, removing guard bands between adjacent sub-carriers. This is possible because the frequencies (sub-carriers) are orthogonal, meaning the peak of one sub-carrier coincides with the null of an adjacent sub-carrier.

In an OFDM system, a very high rate data stream is divided into multiple parallel low rate data streams. Each smaller data stream is then mapped to individual data sub-carrier and modulated using some sorts of PSK (Phase Shift Keying) or QAM (Quadrature Amplitude Modulation). i.e. BPSK, QPSK, 16-QAM, 64-QAM.

OFDM needs less bandwidth than FDM to carry the same amount of information which translates to higher spectral efficiency. Besides a high spectral efficiency, an OFDM system such as WiMAX is more resilient in NLOS environment. It can efficiently overcome interference and frequency-selective fading caused by multipath because equalizing is done on a subset of sub-carriers instead of a single broader carrier. The effect of ISI (Inter Symbol Interference) is suppressed by virtue of a longer symbol period of the parallel OFDM sub-carriers than a single carrier system and the use of a cyclic prefix (CP).
The OFDM spread-spectrum scheme is used for many broadly used applications, including digital TV broadcasting in Australia, Japan and Europe; digital audio broadcasting in Europe; Asynchronous Digital Subscriber Line (ADSL) modems and wireless networking worldwide (IEEE 802.11a/g).
Like OFDM, OFDMA employs multiple closely spaced sub-carriers, but the sub-carriers are divided into groups of sub-carriers. Each group is named a sub-channel. The sub-carriers that form a sub-channel need not be adjacent. In the downlink, a sub-channel may be intended for different receivers. In the uplink, a transmitter may be assigned one or more sub-channels.
Subchannelization defines sub-channels that can be allocated to subscriber stations (SSs) depending on their channel conditions and data requirements. Using subchannelization, within the same time slot a Mobile WiMAX Base Station (BS) can allocate more transmit power to user devices (SSs) with lower SNR (Signal-to-Noise Ratio), and less power to user devices with higher SNR. Subchannelization also enables the BS to allocate higher power to sub-channels assigned to indoor SSs resulting in better in-building coverage.

Subchannelization in the uplink can save a user device transmit power because it can concentrate power only on certain sub-channel(s) allocated to it. This power-saving feature is particularly useful for battery-powered user devices, the likely case in Mobile WiMAX.

The WiMAX forum established that, initially, OFDM-256 will be used for fixed-service 802.16d (2004). It is referred to as the OFDM 256 FFT Mode, which means there are 256 subcarriers available for use in a single channel. Multiple access on one channel is accomplished using TDMA. Alternatively, FDMA may be used.

On the other hand, OFDMA 128/512/1024/2048 FFT Modes have been proposed for IEEE 802.16e (mobile service). OFDMA 1024 FFT matches that of Korea’s WiBRO. OFDM 256 also is supported for compatibility with IEEE 802.16d (fixed, 2004).

3G in 900MHz band can make 3G a winner

The widespread deployment of 3G networks in the 900MHz GSM spectrum band, as well as the 2100MHz band, could enable an additional 300 million people across Asia, Europe and Africa to enjoy mobile broadband services by 2012, according to a study by the analyst and consulting company Ovum for the GSMA.
Note: HSPA is already being deployed at 900MHz in Finland and trials are underway in a number of other countries, such as France and the Isle of Man. More about this is available here.
In 900MHz, the greater range of radio waves in the lower spectrum band and their ability to provide better coverage in buildings would enable operators to achieve much broader 3G coverage, particularly in rural areas. The study shows that a 3G network in the 900MHz band would achieve up to 40% greater coverage than a 3G network in the 2100MHz band for the same capital expenditure.
The cost-effectiveness of 3G at 900MHz would be of particular significance in developing countries, many of which are looking to HSPA, an evolution of the leading 3G technology, to provide high-speed Internet access in the many regions that lack fixed-line infrastructure. However, Ovum cautions that the level of success of 3G in the 900MHz band will depend on multiple countries making this spectrum band available in a harmonised way, so that equipment manufacturers have a large market to target and can quickly achieve economies of scale, particularly for handsets.
Ovum envisages that operators would use 900MHz to provide widespread 3G coverage, supplemented by 3G at 2100MHz in urban ‘hot-spots’ that need more capacity. The extensive use of both the 900MHz and the 2100MHz bands for 3G in Asia–Pacific countries could lead to 450 million people in the region using 3G by 2012, if all operators chose to deploy 3G and the majority of investment goes into 3G at 900MHz. If 3G were restricted to 2100MHz alone, Ovum forecasts there will be just 200 million people using 3G in the region by 2012.
In light of these findings, the GSMA urges regulators, together with vendors, to plan together for the coordinated refarming of 900/1800MHz spectrum, which is widely used for GSM in Europe, Asia and Africa, and for the availability of compatible and affordable handsets. Such global planning will give investors the confidence to fund the development of 3G/HSPA at 900MHz and 1800MHz as well. There should be no differentiation between the different GSM bands (900/1800/1900) to avoid any distortion of competition among GSM operators. The same benefits would also be achieved by refarming 850MHz spectrum (widely used in US and Latin America).
According to the Inquirer, the GSMA may have fallen into a trap. China has its own flavour of 3G – called TD-SCDMA. One of the benefits of this standard – compared to W-CDMA which the GSMA promotes – is that it shares infrastructure costs with existing GSM equipment. Naturally providing cost savings. So while the GSMA is admitting that standard W-CDMA at 2100 MHz is too expensive for developing economies, China can quite reasonably say, "We know. That's why we've stuck with TD-SCDMA.
A bit of an own goal really.

Tuesday, 26 June 2007

OMA seeks to ease mobile TV pain

The Open Mobile Alliance's recently-unveiled BCAST Enabler specification is designed to create a 'write once, run anywhere' environment' for broadcasters and other content providers. The spec - if widely adopted - could have significant implications for the concept of mobile TV 'roaming'.
In theory, it means broadcasters will be able to deploy their programming across the whole gamut of broadcast mobile TV platforms - DVB-H, DVB-SH, DMB, DAB-IP, ATSC-M/H etc - with little or no tweaking.
Because it works with any IP-based content delivery technology BCAST Enabler can also be used for the delivery of programming across cellular systems like 3GPP MBMS, 3GPP2 BCMCS and mobile unicast streaming systems, such as 3G streaming.

What benefits will OMA BCAST offer broadcasters and broadcast network operators?
• The specification enables broadcast-only mode for delivering services. It also allows broadcast-only terminals and free-to-air content with service and content protection capability.

• The specification is agnostic to access network meaning that the same service offering can be delivered over broadcast channel, interaction channel or both. Being agnostic to underlying architecture allows integration of the broadcast offering with operators or independent delivery over the interaction channel, which is controlled by broadcaster.

• Service interactivity is well specified and caters for broad range of services including interactive and direct feedback from viewers. Also, the service interactivity is not bound to the cellular channel – WLAN or a similar network can also be used. The use of the interaction channel allows personalization of services and service guides.

• The Service Guide enables the broadcaster to associate broadcast
programming with on-demand content. In addition, it supports both broadcast and on-demand delivery of the Service Guide itself.

What benefits will OMA BCAST offer terminal manufacturers?

• The Mobile TV Enabler specifies features for a common TV & video service layer that are currently not addressed by other specifications but still needed to ensure interoperability for large-scale terminal availability.

• Enables economies of scale by leveraging same technologies for both
broadcast and interactive channels. This means vendors can build an
economically viable terminal base that can be used by operators/carriers or broadcasters or jointly by both.

Sunday, 24 June 2007

Certified Wireless USB's and Cablefree USB

While doing some background sstudy of Wireless USB i came acrosss interesting information. Apparently there are two different Wireless USB standards that are being developed and they are not compatible with each other. More information aas follows:

Wireless USB (also known as Cablefree USB)

* Supported by UWB forum (pioneered by Freescale semiconductor)

* Uses DS-UWB (direct sequence)

* It mimics USB 2.0 in its interfaces to host and peripheral devices, handling the wireless issues within device adapters.

* This approach of retaining the USB 2.0 protocol means that developers can quickly offer products that users can simply plug in without making any system changes.

* Existing USB drivers will work

* The current Freescale UWB chipset operates at 114Mbps with a likely throughput of 50Mbps

Certified Wireless USB

* Supported by WiMedia alliance and USB-IF (USB Implementers Forum)


* Certified Wireless USB employs a new communications protocol, similar but not identical to USB, to address the wireless issues.

* The Certified Wireless approach, on the other hand, required the definition of a new specification. The initial specification, which its developers released in May 2005, received a supplement defining the association's methods in March 2006. The specifications are now under the control of the USB-IF.

* Will need new software and USB drivers

* They operate at 480Mbps like USB 2.0 with probably similar throughput (peak 320Mbps)

Friday, 22 June 2007

2.5 Billion GSM Subscribers Worldwide

Bellevue, WA, June 05, 2007 -
Today, 3G Americas reports that the number of GSM mobile wireless subscribers worldwide has reached 2.5 billion, a stunning 400% increase in GSM subscribers from only six years ago, according to the estimates of Informa's World Cellular Information Service. Every day, there are more than one million new additions to the GSM family of technology users receiving service from one of 700 commercial GSM networks across 218 countries and territories around the world.

“It’s unprecedented for almost any global industry to achieve the growth and success demonstrated by the GSM family of technologies, with an estimated 2.5 billion global customers today,” stated Chris Pearson, President of 3G Americas. “This level of wireless technology growth exceeds that of almost all other lifestyle-changing innovations.”
Looking back, it was almost one hundred years ago when the first so-called "mobile" phone call was made by Lars Ericsson in 1910— although not wireless, as Ericsson attached wires to a telephone pole terminal to make his call while on the road. 2007 marks the 60th anniversary of AT&T and Bell Laboratories' 1947 invention of the cellular phone. Today, it is estimated that more than 37% of the world's 6.6 billion people (US Census Bureau) use GSM technology.

GSM subscribers, including nearly 130 million UMTS/HSDPA subscriptions, currently comprise nearly 85% of the global mobile wireless market. GSM became the dominant Latin American mobile wireless technology in less than a decade since its launch in the region in 1998, acquiring 2 million subscribers by the year 2000, and 200 million by end of year 2006. The GSM family now serves 331 million customers in all the Americas as of 1Q 2007, and is available in every single country. This market leadership is due to the numerous technical and economic benefits of the GSM family of technologies for both operators and their customers.

GSM technologies, including GPRS, EDGE and UMTS/HSPA, offer overwhelming advantages in terms of global scope, scale, international roaming and service that are still unmatched by other mobile wireless technologies. As of May 2007, there are 169 UMTS operators in service across 71 countries, and 117 of those operators in 59 countries have deployed an enhanced version of UMTS called HSDPA. Additionally, nearly all UMTS/HSDPA devices manufactured today include the EDGE technology as the compatible fallback technology, allowing for global roaming and delivery of high-speed wireless data services.
HSPA (HSDPA/HSUPA) technology is poised to be the leading mobile broadband technology for the rest of the decade, outpacing alternative mobile broadband technologies by leveraging on the current installed base of the GSM family of technologies and providing the most efficient solution. It is expected that almost all GSM/EDGE operators will someday migrate to HSPA technology.

Pearson continued, “While other technologies are grabbing attention, HSPA is being rolled out around the world, separating future promise from that which is available today. Building upon the enormous foundation of customers and commercial deployment of GSM, and the broad research and development by vendors, HSPA will continue in its mobile broadband leadership position for years to come.”

For white papers, statistics and more information on the GSM family of technologies, visit

About 3G Americas: Unifying the Americas through Wireless Technology
The mission of 3G Americas is to promote and facilitate the seamless deployment throughout the Americas of GSM and its evolution to 3G and beyond. The organization fully supports the Third Generation (3G) technology migration strategy to EDGE and UMTS/HSPA adopted by many operators in the Americas. The GSM family of technologies accounts for 85% of wireless mobile customers worldwide. 3G Americas is headquartered in Bellevue, WA with an office for Latin America and the Caribbean in Dallas, TX. For more information, visit our website at

About Informa Telecoms & Media
Informa Telecoms & Media provides business intelligence and strategic services to the global telecoms and media markets. All of our products and services - from news, trend analysis and forecasting to industry data, face-to-face events and training - are driven by our deep understanding of the markets we serve and by our goal to help our clients make better business decisions.

Wednesday, 20 June 2007

Continuous Packet Connectivity (CPC)

Packet-oriented features like HSDPA and HSUPA (HSPA) in UMTS systems provide high data rates forboth downlink and uplink. This will promote the subscribers’ desire for continuous connectivity, where theuser stays connected over a long time span with only occasional active periods of data transmission, andavoiding frequent connection termination and re-establishment with its inherent overhead and delay. Thisis the perceived mode to which a subscriber is accustomed in fixed broadband networks (e.g., DSL) andmay make a significant difference to the user experience.

The Fractional-DPCH feature was introduced in Rel-6 to support a high number of HSDPA users in thecode limited downlink, where effectively a user in the active state, not being transmitted with any data, isconsuming only a very small portion of the downlink capacity.

In the uplink, the limiting factor for supporting a similarly high number of users is the noise rise. For sucha high number of users in the cell it can be assumed that many users are not transmitting any user datafor some time (e.g., for reading during web browsing or in between packets for periodic packettransmission such as VoIP). The corresponding overhead in the noise rise caused by maintained controlchannels will limit the number of users that can be efficiently supported.

Since completely releasing the dedicated connection during periods of traffic inactivity would cause considerable delays for reestablishing data transmission and a correspondingly worse user perception,the Continuous Connectivity for Packet Data Users intends to reduce the impact of control channels onuplink noise rise while maintaining the connections and allowing a much faster reactivation for temporarily inactive users. This is intended to significantly increase the number of packet data users (i.e. HSPA users) in the UMTS FDD system that can stay in the active state (Cell_DCH) over a long time period,without degrading cell throughput. The objective aims also at improving the achievable UL capacity forVoIP users with its inherent periodic transmission through reducing the overhead of the control channels.

Delay optimization for procedures applicable to PS and CS Connections

In Rel-99, UMTS introduced a dedicated channel (DCH) that can be used for CS and PS connectionswhen UE is in CELL_DCH state. In addition to CELL_DCH state, Rel-99 introduced CELL_FACH statewhere signaling and data transmission is possible on common channels (RACH and FACH) andCELL_PCH and URA_PCH states, where the transmission of signaling or user data is not possible butenables UE power savings during inactivity periods maintaining the RRC connection between UE andUTRAN and signaling connection between UE and PS CN. The introduction of the CELL_PCH andURA_PCH states, the need of releasing the RRC connection and moving the UE to Idle mode for PSconnections was removed and thus the Rel-99 UTRAN can provide long living Iu-connection PS services.

On the other hand, when UE is moved to CELL_PCH or URA_PCH state, the start of data transmissionagain after inactivity suffers inherent state transition delay before the data transmission can continue inCELL_DCH state. As new packet-oriented features like HSDPA and HSUPA in Rel-5 and Rel-6 UMTSsystems respectively provide higher data rates for both downlink and uplink in CELL_DCH state, the statetransition delay has been considered to be significant and negatively influencing the end user experience.

In addition to RRC state transition delay, the radio bearer setup delay to activate new PS and CS serviceshas been seen as problematic in UMTS, due to signaling delays on CELL_FACH state where only lowdata rates are available via RACH and FACH, and due to activation time used to synchronize thereconfiguration of the physical and transport channel in CELL_DCH state.

To secure future competitiveness of UMTS and enhance the end user experience even further, the delayoptimization for procedures applicable to PS and CS connections work is targeted to reduce both setuptimes of new PS and CS services and state transition delays to, but still enable, excellent UE powersaving provided by CELL_PCH and URA_PCH states.

During the 3GPP Rel-6 time frame, the work was focused on solutions that can be introduced in a fastmanner on top of existing specifications with limited effects to the existing implementations. In addition,the solutions which allow the Rel-6 features to be used in the most efficient manner were considered.The agreed modifications can be summarized as: introduction of enhanced support of defaultconfigurations, reduced effects of the activation time, and utilization of HSPA for signaling. Thus, fromRel-6 onwards, the signaling radio bearers (SRBs) can be mapped on HSDPA and HSUPA immediatelyin RRC connection setup and default configurations can be used in radio bearer setup message and RRCconnection setup message in a more flexible manner.

The utilization of default configuration and mapping of the SRBs on HSDPA and HSUPA will reducemessage sizes, activation times, and introduce faster transmission channels for the signaling procedures,thereby providing significant enhancement to setup times of PS and CS services compared to Rel-99performance.

In the 3GPP Rel-7 time frame, the work will study methods of improving the performance even further,especially in the area of state transition delays. As the work for Rel-7 is less limited in scope of possiblesolutions, significant improvements to both RRC state transition delays and service setups times are expected.

3GPP TR 25.903: Continuous connectivity for packet data users (Release 7)

3G Americas: Mobile Broadband: The Global Evolution of UMTS/HSPA3GPP Release 7 and Beyond

Housam's Technology blog on CPC

Tuesday, 19 June 2007

Voice call continuity (VCC)

Voice call continuity requires maintaining a voice call when a mobile terminal moves from one cell to another for second generation Global System for Mobile Communications (GSM) digital cellular communications systems. Operational for many years, this technique enables a conversation to continue when the Circuit-Switched (CS) call reroutes to use a new basestation as the mobile moves from one coverage area to another. The parties will perceive no break whatsoever.

Today, the scenario is rather more complicated, with calls being handed over not only from 2G to 2G cells and from 3G to 3G cells, but also between 2G GSM and 3G Universal Mobile Telecommunications System (UMTS) cells. This is relatively easy from an administrative point of view, given that generally the same cellular network is involved throughout.

Earlier work carried out within the 3rd Generation Partnership Project (3GPP) envisaged telephony using packet-switched connections – Voice over Internet Protocol (VoIP) – using either the 3GPP-defined IP Multimedia Subsystem (IMS) on the 3G Universal Terrestrial Access Network (UTRAN), or Wireless Local Area Network (WLAN) radio access technology based on IEEE 802.11, and other standards. This was covered by the WLAN interworking work items.

However, until now, handover between CS and IMS (packet-switched) calls was not addressed. 3GPP is now investigating the problem of handing over a voice (or potentially video or other multimedia conversational service) call between the cellular network and a WLAN, possibly operated by a completely different service provider. Again, for conversational service, the hand-over has to be seamless, with no break in service perceived by either party to the call. Until recently, such handover had only been considered for services that are not real-time, such as file-transfer, where short breaks during the handover process are acceptable and probably go unnoticed by the user.

The approach taken by 3GPP is to have the WLAN operator use the information registered by the home operator for the mobile terminal subscriber in this sequence:

1. Validate the eligibility of the handover to happen at all
2. Manage charging for the call that is effectively transferred from one network operator to another

It is generally, though not necessarily, the case that WLAN hotspots are also well covered by cellular service. Thus, such handover may take place when cellular coverage is reduced to an unacceptable level, yet an adequate WLAN hotspot service is available. The handover is more likely to occur when spare bandwidth exists on the WLAN but where excess demand for cellular channels exists.

The goal is to maintain the conversational service call, thus optimizing the service to the users, which in turn will maximize the revenue accruing to the operator(s). 3GPP embarked on the technical activity required to enable this service by approving a work item on Voice Call Continuity (VCC) in the June 2005 meeting of its Technical Specification Group System Aspects and Architecture (TSG SA). In order to be accepted onto the 3GPP work plan, any work item needs to have the support of at least four supporting member companies, and no sustained opposition. The VCC work item has no fewer than 16 supporters, and its progress
can be tracked on the 3GPP website, It is intended that this work be achieved in the Release 7 time frame.

3GPP TR 23.806: Voice Call Continuity between CS and IMS Study (Release 7)
3GPP TS 23.206: Voice Call Continuity (VCC) between Circuit Switched (CS) and IP Multimedia Subsystem (IMS); Stage 2 (Release 7)
3GPP TS 24.206: Voice Call Continuity between the Circuit-Switched (CS) domain and the IP Multimedia Core Network (CN) (IMS) subsystem; Stage 3 (Release 7)
3GPP TS 24.216: Communication Continuity Management Object (MO) (Release 7),04.pdf

Monday, 18 June 2007

IMS strategies: Synopsis from IMS 2.0 world forum

From Ajit's Open Gardens Blog:

IMS 2.0 world forum is a must attend event .. I learnt a lot from it. Here is a brief synopsis of where I see IMS is heading to ..

Seek your thoughts and feedback especially you can identify other Operators with an interesting strategy and / or if you attended this event

As I could gather, there are six broad strategies:
a) Voice call continuity(VCC) / fixed to mobile convergence
b) Blended voice : voice tied contextually to messaging or rich media
c) SIP without IMS (Naked SIP)
d) Strategies from device manufacturers(especially Nokia and Motorola)
e) Real time IMS applications (multiplayer games and other such applications that need near real time blended media interaction within a session)
f) Abstraction of the core network

Most of the focus is around (a) Voice call continuity(VCC) / fixed to mobile convergence

This is a pity – but also understandable Operators are most familiar with voice
In its broadest sense, voice call continuity pertains to roaming within cellular and non cellular networks(such as roaming between cellular and wifi networks). A specific instance of this is
Fixed to mobile convergence for instance BT fusion

My personal view is:

a) I don’t quite know if I would be interested in FMC as a customer ..
b) I think its being sold on cost – which is not a good idea
c) I think it fulfils an industry goal(fixed and mobile networks trying to get new subscribers from each other’s networks in mature markets)
d) In general, voice is becoming cheap .. so I am not sure that a pure voice play is a good idea

Blended voice(b) and real time applications(e) are interesting but need device support. Devices supporting IMS fully are conspicuous by their absence!

In contrast, devices supporting SIP(c) - but not IMS are very much here and so are applications – for instance

Abstracting the network layer through software APIs(f) – is the most interesting – but I felt very few Operators had the vision to embrace this strategy at the moment. The two big exceptions being TIM and Telia sonera - who are doing some very interesting work.

To recap, by abstracting the network layer, I mean : In an IP world, as the Mobile Internet mirrors the Internet, the Operator should focus on the core of the network and leave the edge of the network to third parties. Specifically, this means – identify the elements that can be performed ONLY in the core and then abstract them through APIs. This approach gets us away from the dichotomy of the ‘pipe’ vs. ‘no pipe’. It also means that the Operator retains control.

Finally, Operators in emerging markets like Globe telecom from Philippines were also impressive i.e. they understood the space, the issues specific to their market and how they could leverage IMS in their markets. Harvey G Libarnes, Head of innovation and incubations program , Globe Telecom, gave a very thorogh presentation

Finally, there are some interesting plays : such as Mobilkom with A1 over IP and France Telecom with IPTV strategy

To conclude:
a) At Operator level, IMS is still largely about voice and a defensive approach(such as FMC)
b) Lack of devices is the key question mark
c) Device manufacturers on the other hand have significant leverage(more on that soon)
d) Some operators are going to be very innovative – TIM and Teliasonera from amongst the attendees

Cognitive radio

Cognitive radio (CR) is a newly emerging technology, which has been recently proposed to implement some kind of intelligence to allow a radio terminal to automatically sense, recognize, and make wise use of any available radio frequency spectrum at a given time. The use of the available frequency spectrum is purely on an opportunity driven basis. In other words, it can utilize any idle spectrum sector for the exchange of information and stop using it the instant the primary user of the spectrum sector needs to use it. Thus, cognitive radio is also sometimes called smart radio, frequency agile radio, police radio, or adaptive software radio,1 and so on. For the same reason, the cognitive radio techniques can, in many cases, exempt licensed use of the spectrum that is otherwise not in use or is lightly used; this is done without infringing upon the rights of licensed users or causing harmful interference to licensed operations.

The only difference with SDR (Software Defined Radio) is that a cognitive radio needs to scan a wide range of frequency spectra before deciding which band to use, instead of a predefined one, as an SDR terminal does. One of the most important characteristic features of an SDR terminal is that its signal is processed almost completely in the digital domain, needing very little analogue circuit. This brings a tremendous benefit to make the terminal very flexible (for a multimode terminal) and ultrasmall size with the help of state-of-the-art microelectronics technology.

More Information at:

Friday, 15 June 2007

AT&T bets on LTE

AT&T says its next-generation roadmap leads to LTE, though it's evaluating the use of WiMAX technology for backhaul according to a report in Wireless Week.
AT&T's Chris Hill, vice president of Government Solutions for Mobility, commented during an interview at the Wireless Communications Association (WCA) conference that, "LTE provides similar throughputs, so we're taking a wait-and-see approach to WiMAX. We just don't see the value proposition for mobile WiMAX."
After reading this i started digging around on who is betting on WiMAX and i found an excellent summary:
Mobile wimax equipment which utilize beam-forming and MIMO technologies will become available towards the end of this year. Broadband wireless deployments using pre-802.16e compliant equipment have already begun. In Korea both KT and SK Telecom have implemented mobile broadband wireless networks in specific locations throughout the country.

Sprint/Nextel are deploying an 802.16e compliant mobile wimax network which will reach 100 million Americans by the end of 2008. BT will bid for 2.5GHz RF spectrum in the Ofcom auctions which will take place towards the end of the year 2007. Gaining such spectrum will allow the incumbent to deploy an efficient wimax service and compete with companies such as Vodafone for triple play services. Cable companies are gradually acquiring spectrum and are looking at distributing their content to mobile devices. Greenfield operators are expected to utilize mobile wimax technology in order to secure a 3G/4G market position by attracting consumers with an early new level of service. Clearwire is such a carrier with operations in the United States, Denmark, Belgium, Ireland and in Mexico (via MVSnet).

Equipment manufacturers are becoming increasingly active in mobile wimax. Vendors such as Samsung, Nortel Networks, Alcatel and Nokia-Siemens Networks are all involved in 802.16e projects globally. Motorola have just announced a major deal in Pakistan. Companies that have been heavily involved in operator proprietary broadband wireless implementations such as Alvarion and Proxim are also developing 802.16e compliant platforms. Various chipset providers such as Wavesat, Runcom Technologies and Beceem Communications are developing OFDMA chips and are testing their products for interoperability with solutions from other vendors. Dual mode handsets will be very popular with mobile wimax deployments with GSM/OFDMA and CDMA/OFDMA handsets dominating the market.

But there is confusion. Ericsson believe that by the year 2010 mobile wimax will account for only 5-10% of global broadband wireless revenues and are therefore more focused on broadband cellular technologies. Who is right? Availability of 2.5GHz spectrum is crucial to the success of mobile wimax particularly throughout the western world. In Europe HSPA is dominating the cellular market and this combined with the current unavailability of 2.5GHz spectrum throughout most of the continent is leading to little interest from mobile operators. In the U.S a lot of the 2.5GHz spectrum is owned by Sprint. The carrier will start its deployment by using 10MHz channels to deliver services and could use even larger bandwidths in the future.
Meanwhile in the US, everyone is concentrating on the 700MHz spectrum auction that will be happening soon. The spectrum is in the upper 700 MHz range, not the lower 700 MHz band where companies such as Qualcomm’s MediaFLO already are deploying services. It’s desirable for wireless carriers because at 700 MHz, fewer base stations are required than at higher ranges, making it more economical for buildouts. But numerous other parties also are interested in the spectrum, as evidenced in FCC filings. Everyone from Cyren Call Communications to Frontline Wireless and Google are giving advice on how to use the spectrum.
Among the more neutral players in the cacophony of lobbyists trying to affect the outcome of the auction is Nortel. The company has been sending executives to Washington, D.C., mainly to serve as educators around technologies that could be deployed in the space. Those include OFDM/MIMO and others around WiMAX, as well as evolutions of the GSM and CDMA technologies in long-term evolution (LTE) and ultramobile broadband (UMB), respectively.

“We are keeping a very close eye on where the 700 MHz auction goes,” says Danny Locklear, director of Nortel wireless product marketing. “We see this 700 MHz space as being a very large opportunity for us,” as well as for the overall U.S. market, where it will add more competition and improvements for end-users.

It’s important for companies like Nortel to be involved now, he explains, because typically there is an 18-month cycle from the time standards are developed to the actual product. Delivering products for a new or different band of spectrum is nothing new; vendors know how to do it, but it still takes time, not only in the hardware but software as well.

Discussions over 700 MHz are expected to continue through the coming months, with a final ruling possibly toward the end of the summer and an auction start time anywhere between the third quarter of this year and January of next year. Even then, some of the winners of the spectrum probably won’t be moving in immediately. Analog TV users currently in the spectrum have until the first quarter of 2009 to vacate.