Dual-Cell HSPA in Release 8 and beyond

Some interesting developments are ongoing in the 3GPP standardisation from Release-8 onwards. You must be aware that the current bandwidth in UMTS/HSPA is 5 MHz. Since most of the operators generally won bigger chunk of spectrum of contiguous 5MHz band, they can actually combine these chunks to create a larger spectrum and hence increase data rates.

In Release 8 in downlink, it is possible to increase data rates using either a combination of MIMO and 64QAM or dual-cell HSDPA for operation on two 5MHz carriers with 64QAM, data rates reach up to 42Mbps.

In deployments where multiple downlink carriers are available, the new multicarrier operation offers an attractive way of increasing coverage for high bit rates. Rel-8 introduces dual-carrier operation in the downlink on adjacent carriers. This technique doubles the peak rate from 21Mbps to 42Mbps without the use of MIMO – it doubles the rate for users with typical bursty traffic; therefore, it also doubles the average user throughput, which translates into a substantial increase in cell capacity.

You may remember that I mentioned earlier that the operators are not too keen on going for MIMO for non-LTE technology. This is because they will have to upgrade their hardware and the antennas which could increase their cost significantly for a technology that is not going to be around for long.

Another thing to note before it becomes too confusing is that there are two terms for 'DC' being used right now. One of them is 'Dual Carrier' and other is 'Dual Cell'. In Release 8, the term being used is Dual-Cell for HSDPA which is also known as DC-HSDPA. The Technical specification to follow is 3GPP, TR 25.825 “Dual-Cell HSDPA operation” V1.0.0, May 2008.

The Dual-Cell assumes that both the 5MHz bands are contiguous. If they are not then the better term to refer for DC is Dual-Carrier.

A dual-carrier user can be scheduled in the primary serving cell as well as in a secondary serving cell over two parallel HS-DSCH transport channels. All non-HSDPA-related channels reside in the primary serving cell, and all physical layer procedures are essentially based on the primary serving cell. Either carrier can be configured to function as the primary serving cell for a particular user. As a consequence, the dual-carrier feature also facilitates an efficient load balancing between carriers in one sector. As with MIMO, the two transport channels perform hybrid automatic repeat request (HARQ) retransmissions, coding and modulation independently. A difference compared to MIMO is that the two transport blocks can be transmitted on their respective carriers using a different number of channelization codes. In terms of complexity, adding a dual-carrier receiver to UEs is roughly comparable to adding a MIMO receiver. Because the two 5MHz carriers are adjacent, they can be received using a single 10MHz radio receiver, which is already be available if the UE is LTE-capable.

Following the introduction in Release 8 of dual-carrier operation in the downlink, 3GPP is now discussing operation on multiple 5MHz carriers. Multiband operation of multiple carriers allows a single user to simultaneously aggregate and use the spectrum distributed over different bands. This gives operators greater fl exibility when using available spectrum. Increasing the number of carriers that UEs receive from two to four doubles the peak rate and achievable user throughput. For bursty traffic, this translates into substantially greater capacity, either as a larger number of users at a given data rate, or as a higher data rate for a given number of users. To substantially boost spectral effi ciency, 3GPP is studying the combination of dual-carrier operation and MIMO with 64QAM in the downlink, thereby doubling the peak data rate to 84Mbps. Similarly, they are studying the combination of MIMO, 64QAM and up to four downlink carriers to support peak data rates of more than 100Mbps. The support for UE reception on two frequency bands is an enabler to DC-HSDPA for operators who do not have adjacent 5MHz carriers available in one band, and is therefore of key importance for the further evolution of multi carrier HSPA.

As a consequence of increased data rates in downlink, the uplink data rates need to be improved too. From the aggregation of multiple FDD downlink carriers, the paired FDD uplink carriers can be utilized for improved uplink transmissions. 3GPP studies the usage of two adjacent 5MHz carriers for dual carrier uplink transmissions (DC-HSUPA) supporting data rates of up to 23Mbps. A further benefit of utilizing two uplink carriers is the possibility to support more efficient load balancing in the uplink direction.

In summary, uplink multicarrier operation increases availability as well as coverage of high data rates in the uplink.

In Conclusion, Rel-8 defines improvements in HSPA to achieve higher rates through dual carrier or combined 64QAM+MIMO operation. With the Rel-8 specification nearing completion (targeted for March 2009), planning is already under way in 3GPP for Rel-9 and Rel-10. Further multi-carrier and MIMO options are being explored for HSPA in Rel-9 and Rel-10

If you want to explore this topic further see:

• Nomor research White Paper – Dual Cell HSDPA and its Future Evolution.
• WirelessMoves - Dual Carrier HSDPA - The Push Beyond 5 MHz
• Ericsson - Continued HSPA Evolution of mobile broadband

Mobile broadband to get cheaper

The operators have now got an opportunity to get out of this rat race of constantly upgrading their networks. An article in Broadband Genie mentioned that because of recession operators may delay upgrading their network. The situation reminds me of the time when 3G rollouts were announced.

The operators who spent billions on 3G spectrum didn't seemed very keen on rolling out a network and except '3' which was a greenfield operator in many European markets, most operators took their time to roll out 3G. Those operators have now caught up with others in HSPA rollouts. The same situation is likely to occur in LTE rollouts.

The interesting thing that we have to remember though is that when 3G was being rolled out, there was only one main existing technology called GSM and people used to use dialup connections and we were not hooked on broadband. Now there are many competing technologies vying for the broadband users. We have WiMAX that will be the main competitor and iBurst and WiFi is very common as well. WiFi is free or is available at really low rates, the difficulty being to find one. Recently Inmarsat launched mobile broadband via satellite across the whole of Australia so this is another possibility for Mobile broadband.

If you look at all the options above it is difficult to see how the operators will be able to raise the prices. The only option for it is to go down. Its not difficult for them if they price it properly and optimise their networks. Going back to the Broadband Genie article there was an interesting observation:

Broadband Genie believes that, while pricing models are certainly going to change, it may not be a bad thing for everyone, as heavy users will be charged for the amount they download and less bandwidth intensive consumers may see prices fall.

So in the long term the prices of broadband will come down but at the same time there will be more applications requiring mobile internet use thus increasing our appetite to consume more and maybe the prices will increase for those heavy users. In the meantime enjoy your mobile broadband.

"Upskirting" with mobiles

First there was Sexting and now I came across Upskirting. Apparently hundreds of thousands of photographs taken up unsuspecting women's skirts being posted online, the practice of 'upskirting' is clearly on the rise.

It is impossible to judge how many women have been victims of upskirting, though a quick internet search yields hundreds of sites with hundreds of thousands of images. And there may be millions more pictures on phones and laptops that have never been shared. They have been taken in the street, on escalators in shopping centres, on trains, at bus stops and in supermarkets, schools, offices and nightclubs.

Upskirt photography is also routinely used by paparazzi photographers. Usually taken as a woman steps out of a car, "crotch shots" are prized by newspapers such as the Daily Sport and countless gossip and porn websites. While it is often assumed that a handful of celebrities, such as Britney Spears and Paris Hilton, actively encourage upskirt shots, many famous women are deeply upset by the prospect. In a recent interview, the Harry Potter actor Emma Watson described how, on a night out to celebrate her 18th birthday, "I realised that overnight I'd become fair game." (The rules that govern photographs of people under 18 are stricter than those for adults.) "One photographer lay down on the floor to get a shot up my skirt ... The night it was legal for them to do it, they did it. I woke up the next day and felt completely violated by it all."

There are endless web forums where "amateur" upskirters can exchange tips on how to get the "best" pictures. One was posted by a man who had made a "cam-bag" - a holdall with a specially made pocket with a hole in it for a digital video camera lens. Another writes: "Never forget to shoot their faces before or after to know which girls the ass belongs to ... After the first 50 asses, they look very similar and you lose most of the fun. After upskirting them, either step back and wait for them to turn or step by them and shoot direckly [sic] sidewise." Another poster, who says he operates "mostly at theme parks and tourist hotspots, or really anywhere that draws a large crowd of spectators and cameras", walks around until he finds "an attractive young lady, preferably a teen for my tastes, and then I evaluate the situation." He will often sit down next to a young woman and surreptitiously film her while pretending to fumble for new camera batteries in his bag.

On yet another site, one man posts: "I've been upskirting chicks, mostly at clubs, for almost two years. The club I go to is a great spot, real crowded, strobe lights going, loud music, so no one notices me sitting near the edge of the dance floor and if a woman in a skirt ends up by me I stick the cam under and snap."

In this country (UK), there is no specific legislation against upskirt photography, though it is covered by other laws. "If the person being photographed is in a place which would reasonably be expected to provide privacy in the circumstances, it may amount to the offence of voyeurism under the Sexual Offences Act 2003," says Linda Macpherson, a lecturer on law and expert on legal aspects of photography. "A person convicted of this offence may also be placed on the sex offenders register."

It could also come under the criminal offence of "outraging public decency". Macpherson cites the 2007 case of Simon Hamilton, a barrister, who was convicted after secretly filming up the skirts of women in supermarkets. "He appealed on the basis that, as none of the victims had been aware of the filming and no one else had seen it, public decency could not have been outraged. However, the court of appeal held that it was sufficient that the lewd act had occurred in a public place, and that there were at least two persons present capable of seeing it even if they had not actually seen it."

Repeat offender Andrew Mackie was this month jailed for one year for taking photographs of women in Sunderland and Durham city centres, and breaching a sexual offences prevention order which forbade him from owning a camera after he was convicted of similar offences in 2006.

A lesser sentence, however, was given to Guy Knight, a former chartered accountant from Seaford in East Sussex. He took photographs up women's skirts on trains over a five-month period while commuting to work. He was caught after suspicious passengers reported him to the police. More than 200 illicit images were found on his phone and laptop. Ten of the women in the pictures were traced by police, none of whom were aware they'd been photographed. Last year, he was fined £500 and ordered to pay £500 costs. Detective Constable Bob Cager was reported to have been "extremely disappointed - we thought he would have received a heavier sentence".

While the image of the "Peeping Tom" may seem quintessentially British, upskirting is not confined to the UK. In the US, where many of the images posted on the internet were taken, a recent incident led to a change in one state's law. In Oklahoma in 2007, charges against a 34-year-old man, who had been arrested for kneeling behind a 16-year-old girl in a shop, placing a camera under her skirt and taking a photograph, were dismissed after an appeals court concluded that "the person photographed was not in a place where she had a reasonable expectation of privacy". But in response to local outrage, the law was extended, making the photography of another person without their consent for "prurient, lewd or lascivious purposes" illegal.

In Japan, upskirting is so rife that all mobile phones sold now make a sound that cannot be turned off when a photograph is taken. And several Australian states have specific laws banning upskirt or down-blouse photography.

For women who have become aware of such pictures being taken of them, "it can be extremely distressing," says a spokesperson from Victim Support. "The sense of violation can be the same as with other forms of sexual assault. We would encourage anyone who has been a victim to contact us." Parkinson says of her experience, "I felt unsettled, targeted, and helpless; there was nothing that could be done about what had happened, and nothing I could do to prevent it from happening again."

The "defence" used by some upskirters is that since the majority of shots are taken without the woman's knowledge, and there is usually no way she can be identified to the wider public, there is no "victim". But Sasha Rakoff, director of Object, a group that campaigns against the objectification of women, says it is symptomatic of the perceived notion that women's bodies are public property. "You see upskirt shots on the front of the Sport newspaper and lads' mags, which consistently promote Peeping Toms by printing pictures of readers' girlfriends, and glamour models in "private" settings, such as the shower. Is it any wonder that men - equipped with the latest, cheap and readily-available 'mobile spyware' - then enact real-life voyeurism?

"Whatever barriers might exist to being a Peeping Tom have been comprehensively eroded by the male-orientated media, while men who already had no qualms over this form of sexual invasion are routinely vindicated in their belief that such behaviour is acceptable."

Off on Holidays

Off on holidays, so:

• No new posts
• No news comments approved

See you in a week and bit.

Whitepaper: Mobile Broadband Evolution

3G Americas has released this new paper that can be downloaded from here.

An extract of what it contains from its preface:

This new 2009 paper, The Mobile Broadband Evolution: 3GPP Release 8 and Beyond provides detailed discussions on the HSPA+ enhancements in Rel-8 as well as the EPS, EPC and LTE architecture, features/capabilities and performance estimates. The paper also addresses 3GPP planning for Rel-9 and Rel-10 content which has already begun. In addition to further enhancements to Evolved HSPA or HSPA+, Rel-9 will be focused on features that enhance upon the Rel-8 EPC/LTE capabilities in areas such as location, emergency and broadcast services, support of CS over LTE, Home NodeB/eNodeB architecture considerations (i.e. support for femtocell type applications) and IMS evolution. Further, a new study item in 3GPP will define evolution of the LTE technology to meet IMT-Advanced requirements (called LTE-Advanced), at the same time as work is commencing on the above Rel-9 enhancements. 3GPP recognizes the need to develop a solution and specification to be submitted to the International Telecommunication Union (ITU) for meeting the IMT-Advanced requirements, and therefore, in parallel with Rel-9 work, 3GPP is working on the LTE-Advanced study item which is likely to define the bulk of the content for Rel-10. The white paper The Mobile Broadband Evolution: 3GPP Release 8 and Beyond includes discussion of Rel-10 and what requirements will officially define "4G" technologies with the significant new technology enhancements to EPC/LTE for meeting the very aggressive IMT-Advanced requirements.

3GPP Humour with MIMO ;)

TSG-RAN WG1 Meeting #56 R1-091041
Athens, Greece, 9 – 13 February, 2009

Source: MIMO Very Late Session
Title: Text proposal for TR36.814 on M.I.M.O.
Agenda Item: 12
Document for: Text Proposal


During offline discussion after the parallel session on Agenda Items 12.3 and 12.4, the very late session attendees arrived at the following text proposal for inclusion into TR 36.814.

--- Start text proposal ---
Annex B1: M.I.M.O. (Informative)

B1.1 Scope

The following section describes the M.I.M.O. approach and is best understood in conjunction with the tune of the song “Y.M.C.A.” performed by Village People played in the background.

B1.2 Lyrics

U-E, when your channel looks fine,
I said, U-E, give the network a sign,
Which means, U-E, give a high C-Q-I,
To report what you have measured.

U-E, there is data for you,
And two codewords,
I think they may come through,
So let's put them onto different ports
And use spatial multiplexing.

In other words it is M-I-M-O.
In other words it is M-I-M-O.
You don't need M-L-D,
There are plenty of ways,
Manufacturers have a choice ...

M-I-M-O.
In other words it is M-I-M-O.
Two antennas you need,
Four by four is agreed,
And your throughput can be so high!

U-E, can you see the Node-B?
Come on, U-E, should it do T-x-D?
Alamouti is a simple approach.
But you've got to know this one thing!

Node-B is not serving just you.
I said, Node-B, has a whole cell to do,
And at cell-edge there's no M-I-M-O
'Cause the S-I-N-R is low.

You cannot always do M-I-M-O.
You cannot always do M-I-M-O.
Two R-x ports you have
So you still can combine,
And the coverage should be fine ...

M-I-M-O.
It's good for you to use M-I-M-O.
Two antennas you need,
Four by four is agreed,
And your throughput can be so high!

U-E, if you want to transmit,
I say, U-E, MI-MO isn’t legit,
You will have to wait for L-T-E- A,
Where RAN-1 will make it okay.

That’s where the decisions are made,
And where many MI-MO sessions run late,
So that Dirk says: ‘Juho will you take care
Of this bunch of loopy people?’.

It's fun to standardize M-I-M-O.
It's fun to specify M-I-M-O.
You don't need M-L-D
There are plenty of ways,
Manufacturers have a choice ...

M-I-M-O.
It's fun to specify M-I-M-O.
When your channel looks fine,
Give the network a sign.

M-I-M-O.
Then just go and do M-I-M-O.
Can you see the Node-B?
Should it do T-x-D?

M-I-M-O.

--- End text proposal ---

LTE UE Modes of Operation

From 3GPP TS 24.301, section 4.3:

UE mode of operation

A UE attached for EPS services may operate in one of the following operation modes:

- PS mode of operation: the UE registers only to EPS services;

- CS/PS mode 1 of operation: the UE is CS fallback capable and configured to use CS fallback, and non-EPS services are preferred. The UE registers to both EPS and non-EPS services; and

- CS/PS mode 2 of operation: the UE is CS fallback capable and configured to use CS fallback, and EPS services are preferred. The UE registers to both EPS and non-EPS services.

E-books readers: Good or Bad?

Quite a shocking news item from Guardian:

My iLiad ebook reader is sleek and beautiful. It's a pleasant object to hold, and with its useful page-turning bar, one-handed reading is simple. The matt non-backlit screen is easy on the eye, the design is elegant and unfussy, and it is simple to make notes in the text using the stylus, or to make the font larger or smaller. Perhaps my attachment to the physical form of the book was a little childish. After all, the words are the same whatever format I read them in, and surely it's the words that matter.

It's been striking to me how many book-lovers can immediately see the use of an ebook reader. I've taken my iLiad to writers' gatherings, book launches and meetings with editors. The very people I'd have expected to resist it - bookish people, who both read and write a lot - are the people who have looked at it, played with it, cooed over it and said decisively, "I need one of these." If these people take to the ebook reader with ease, the future of books may indeed be electronic.

And will this be a good thing for the environment? It's hard to judge. A report by the US book industry study group last year found that producing the average book releases more than 4kg of carbon dioxide into the atmosphere - that's the equivalent of flying about 20 miles. Then there's the cost of warehousing and transport to consider and the waste and toxic chemicals produced by paper mils.

What about the electronic alternative? While the digital books themselves have a relatively low impact - recent figures suggest that transferring one produces around 0.1g of CO2 - there are other factors to take into account. Charging the reader and turning virtual pages all have an energy cost, as does turning on your computer and downloading a file. Even so, the balance may still favour the hi-tech alternative. A 2003 study by the University of Michigan concluded that "electricity generation for an e-reader had less of an environmental impact than paper production for the conventional book system".

The heaviest burden, though, will be in making the reader itself. If one were to buy an ebook reader, then keep it for 30 years, the impact would be small. But many electronic devices don't last that long, and with the constant advances in processing power and functionality it's unlikely that we would want to keep a single ebook reader as long as we might keep a book.

Disposal of electronic items is extremely problematic. More than 6m electronic items are thrown away in the UK every year, and the cadmium from one discarded mobile phone is enough to pollute 600,000 litres of water. Even recycling electronic equipment - or processing them into constituent parts - isn't without environmental damage. A recent study by Hong Kong Baptist University examining the environment around a Chinese village intensely involved in e-waste recycling, showed that lead levels in the area - including schools - were raised to an extent that might be dangerous. Paper books are, at least, eventually biodegradable, while ebook readers might pose a lasting environmental problem.

Read the complete article here.

Mobile TV: Any Luck?

Mobile TV, once touted as 'the technology' does not yet seem to be having any luck.

Mobile television suffered another setback when the U.S. House of Representatives voted Wednesday to delay the broadcast airwaves' long-planned transition to all-digital services from Feb. 17 to June 12, a move that effectively forces Qualcomm to postpone plans to increase its MediaFLO TV footprint until early summer. Qualcomm previously said it would turn on FLO TV service in more than 40 additional U.S. cities on Feb. 17, an expansion timed to coincide with a federal law mandating that all full-power television stations must terminate analog broadcasting on that date. The transition to digital television frees up the 700 MHz spectrum auctioned last year by the FCC--Qualcomm spent more than $500 million acquiring eight licenses during the auction, and hopes to serve about 200 million potential mobile TV subscribers in more than 100 U.S. markets by the close of 2009. But with the Nielsen Company estimating that 6.5 million American households remain unprepared for the switch to digital TV, and Congress mulling a stimulus package that includes as much as $650 million in financing for coupons to ease the transition, Qualcomm must now sit tight for four additional months.

According to a report from Nielsen Mobile, only 5% of all U.S. cell phone owners subscribe to a mobile TV service. Yet that number is the highest out of of all the other worldwide markets tracked by the company. Only France and Italy came close, each at 4 percent. According to Nielsen, mobile video use isn't more prevalent due to lack of differentiating capabilities, high cost, and lack of compelling content. In fact, we are now even seeing mobile video's plateau - a point where you would normally expect to see adoption slow considerably.

In the U.S., 10.3 million mobile phone subscribers watch video content on their mobile phones each month. These clips from mobile web sites, subscriptions delivered by the carrier, or through mobile "live" TV programming. But the mobile video subscription market has barely grown during the past year. In Q3 2007 it was at 6.4 percent and by Q3 2008 it was only 7.3 percent. And only 26% of subscribers who paid for mobile video services during the third quarter of 2008 used them at least once a month.

The Open Mobile Video Coalition (OMVC), announced that a new mobile DTV service will soon arrive in 22 U.S. cities, covering 35% of U.S. television households. The mobile service aims to provide live, local and national over-the-air digital television to mobile devices.

Included in the service are 63 stations from the 25 major broadcasters that are on board. Those include NBC Television, Gannett Broadcasting, Sinclair Broadcast Group, Fox Television, Belo Corp., Grey Television, Scripps Television, Hearst Argyle Television, ION Media Networks and Lin Television.

This mobile TV service may succeed where others have failed because it bypasses the carriers altogether. Instead, the service uses an ATSC broadcasting system to beam signals directly from the station to the mobile devices themselves. This unburdens the carriers from having to support the data transmissions - they just have to sell the phones.

If France doesn't decide to go down the DVB-H route, there are many who think that could signal the end of the road for the mobile broadcast standard in most European markets
According to one industry commentator, there's a lot riding on the French. Our source, who would rather not be named, thinks that if the French market does not decide to follow the DVB-H standard this year, then that could be the end for the mobile broadcast standard in the region as a whole.

Certainly, the signs have not been good elsewhere - and the industry is dogged by accusations of self-interest. For example, despite operator pressure, Nokia, which sits on 40-50% market share in most European markets, has not moved as fast as the industry had hoped to push DVB-H and DRM technology into its handsets.

According to the head end vendors, and this is a surprisingly widely held view, the issue has been that Nokia has tried to tie the sale of its network infrastructure to the development of its handset range.

"Nokia is saying, give us the head end, and we will give you the handsets," one competing vendor told us.

The China Digital Television Terrestrial Broadcasting (DTTB) System Standard, also known as GB20600-2006, became the mandatory national DTTB standard in August 2007.

GB20600-2006 was designed to deliver a consistent, high-quality digital TV viewing experience no matter where consumers are sitting: in their living room watching television or on a high-speed train watching shows on their cell phones. The technology can broadcast audio and video at transmission rates of greater than 24 Mbps to consumer devices. Because the mobile reception capability is inherently built into the standard, these consumer devices now have a mobile TV feature that works not only when stationary, but even while traveling at speeds greater than 200 km per hour.

The China television market is in the midst of a broadcast revolution because of this new free-to-air terrestrial DTV standard. GB20600-2006 is spurring station owners to broadcast HDTV signals to TVs and set-top boxes, creating a market opportunity that is larger than any other in the world. With 380 million television households, China is home to more televisions than any other country in the world. And nearly 70 percent of those households receive their programming via roof-top antenna.

At the same time, the GB20600-2006 standard is creating a significant new market for mobile TV services. There are more than 600 million cell phone subscribers in China and nearly seven million new mobile phones are purchased each month. Now that the free-to-air HDTV broadcast signal has become a reality, manufacturers of cell phones and other handheld mobile devices are rushing to incorporate mobile TV reception into their products.

Technical details are available here.

China also has its mobile specific TV standard called the CMMB (China Multimedia Mobile Broadcasting). Leading mobile TV chip-maker Siano Mobile Silicon's CMMB receiver chip, the SMS1180, has been selected to power CMMB mobile TV for leading Chinese phone-makers ZTE, Tianyu, CEC Telecom and MP3/4 giant AIGO.

The number of mobile TV subscribers in Korea grew by almost 60% in 2008 following aggressive marketing campaigns and the Beijing Olympics, reports the Yonhap News Agency.

The number of DMB users totalled 17.25 million at the end of 2008, up 59.9% from a year earlier, according to the Terrestrial-DMB Special Committee. South Korea started the world’s first DMB service in 2005, operated through terrestrial and satellite broadcasts.

According to the committee, which represents six service carriers, 15.4 million terrestrial DMB devices, including mobile phones, were sold as of the end of 2008, up 70% from the previous year. The number of subscribers to the satellite platforms (S-DMB) rose 45% annually to 1.85 million last year.

Telegent Systems announced that it has shipped more than 20 million mobile TV receivers since it launched the products in 2007.

The TV receivers have been rapidly adopted by consumers who want to watch the same TV on their mobiles that they enjoy on their home TVs.

Telegent’s receivers use the existing broadcast infrastructure, and allow consumers to watch local programming.

Telegent’s latest success is a deal with Telefónica Móviles Perú, to bring mobile TV to Telefónica’s ZTE i766 handset.

In order to continue its rapid growth, Telegent is expanding into the PC TV market in 2009 and adopting the digital standard DVB-T.

OFDM and SC-FDMA

OFDM has been around since the mid 1960s and is now used in a number of non-cellular wireless systems such as Digital Video Broadcast (DVB), Digital Audio Broadcast (DAB), Asymmetric Digital Subscriber Line (ADSL) and some of the 802.11 family of Wi-Fi standards. OFDM’s adoption into mobile wireless has been delayed for two main reasons. The first is the sheer processing power which is required to perform the necessary FFT operations. However, the continuing advance of signal processing technology means that this is no longer a reason to avoid OFDM, and it now forms the basis of the LTE downlink. The other reason OFDM has been avoided in mobile systems is the very high peak to average ratio (PAR) signals it creates due to the parallel transmission of many hundreds of closely-spaced subcarriers. For mobile devices this high PAR is problematic for both power amplifier design and battery consumption, and it is this concern which led 3GPP to develop the new SC-FDMA transmission scheme.

The LTE downlink transmission scheme is based on OFDM. OFDM is an attractive downlink transmission scheme for several reasons. Due to the relatively long OFDM symbol time in combination with a cyclic prefix, OFDM provides a high degree of robustness against channel frequency selectivity. Although signal corruption due to a frequency-selective channel can, in principle, be handled by equalization at the receiver side, the complexity of the equalization starts to become unattractively high for implementation in a mobile terminal at bandwidths above 5 MHz. Therefore, OFDM with its inherent robustness to frequency-selective fading is attractive for the downlink, especially when combined with spatial multiplexing.

Additional benefits with OFDM include:
• OFDM provides access to the frequency domain, thereby enabling an additional degree of freedom to the channel-dependent scheduler compared to HSPA.
• Flexible bandwidth allocations are easily supported by OFDM, at least from a baseband perspective, by varying the number of OFDM subcarriers used for transmission. Note, however, that support of multiple spectrum allocations also require flexible RF filtering, an operation to which the exact transmission scheme is irrelevant. Nevertheless, maintaining the same baseband-processing structure, regardless of the bandwidth, eases the terminal implementation.
• Broadcast/multicast transmission, where the same information is transmitted from multiple base stations, is straightforward with OFDM.

For the LTE uplink, single-carrier transmission based on DFT-spread OFDM (DFTS-OFDM) is used. The use of single-carrier modulation in the uplink is motivated by the lower peak-to-average ratio of the transmitted signal compared to multi-carrier transmission such as OFDM. The smaller the peak-to-average ratio of the transmitted signal, the higher the average transmission power can be for a given power amplifier. Single-carrier transmission therefore allows for more efficient usage of the power amplifier, which translates into an increased coverage. This is especially important for the power-limited terminal. At the same time, the equalization required to handle corruption of the single-carrier signal due to frequency-selective fading is less of an issue in the uplink due to fewer restrictions in signal-processing resources at the base station compared to the mobile terminal.

In contrast to the non-orthogonal WCDMA/HSPA uplink, which also is based on single-carrier transmission, the uplink in LTE is based on orthogonal separation of users in time and frequency. Orthogonal user separation is in many cases beneficial as it avoids intra-cell interference. However allocating a very large instantaneous bandwidth resource to a single user is not an efficient strategy in situations where the data rate mainly is limited by the transmission power rather than the bandwidth. In such situations, a terminal is typically allocated only a part of the total transmission bandwidth and other terminals can transmit in parallel on the remaining part of the spectrum. Thus, as the LTE uplink contains a frequency-domain multiple-access component, the LTE uplink transmission scheme is sometimes also referred to as Single-Carrier FDMA (SC-FDMA).

Via: 'Agilent Whitepaper' and '3G evolution'.