Orthogonality and non orthogonality

Multiple access (MA) is a basic function in wireless cellular systems. Generally speaking, MA techniques can be classified into orthogonal and non-orthogonal approaches. In orthogonal approaches, signals from different users are orthogonal to each other, i.e., their cross correlation is zero, which can be achieved by time division multiple-access (TDMA), frequency-division multiple-access (FDMA) and orthogonal-frequency division multiple-access (OFDMA). Non-orthogonal schemes allow non-zero cross correlation among the signals from different users, such as in random waveform code-division multiple-access (CDMA), trellis-coded multiple-access (TCMA) and interleave-division multiple-access (IDMA).

First and second generation cellular systems are dominated by orthogonal MA approaches. The main advantage of these approaches is the avoidance of intra-cell interference. However, careful cell planning is necessary in these systems to curtail cross-cell interference. In particular, sufficient distance must exist between re-used channels, resulting in reduced cellular spectral efficiency.

Non-orthogonal CDMA techniques have been adopted in second and third generation cellular systems (e.g. CDMA2000 and uplink WCDMA). Compared with its orthogonal counterparts, CDMA is more robust against fading and cross-cell interference, but is prone to intracell interference. Due to its spread-spectrum nature, CDMA is inconvenient for data services (e.g., wireless local area networks (WLANs) and 3GPP high speed uplink/downlink packet access (HSUPA/HSDPA) standard) that require high single-user rates.

Communication services can be classified into delay sensitive and insensitive ones. A typical example of a delay-insensitive service is email. Typical examples of delay-sensitive services include speech and video applications. For delay insensitive services, rate constraints are relatively relaxed for individual users and maximizing the throughput by orthogonal methods is a common strategy. The maximum throughput can be achieved by a one-user transmission policy, where only the user with the largest channel gain is allowed to transmit. This implies time domain orthogonality as adopted in many WLANs. For delay-sensitive services, on the other hand, each user must transmit a certain amount of information within a certain period and maximizing the throughput is no longer an appropriate strategy. Rate constraints must be considered in this case.

CDMA is the most well known non-orthogonal technique. The main advantages of CDMA are its robustness against fading and cross-cell interference, and its flexibility in asynchronous transmission environments.

An uplink data transfer mechanism in the HSUPA is provided by physical HSUPA channels, such as an Enhanced Dedicated Physical Data Channel (E-DPDCH), implemented on top of Wideband Code Division Multiple Access (WCDMA) uplink physical data channels such as a Dedicated Physical Control Channel (DPCCH) and a Dedicated Physical Data Channel (DPDCH), thus sharing radio resources, such as power resources, with the WCDMA uplink physical data channels. The sharing of the radio resources results in inflexibility in radio resource allocation to the physical HSUPA channels and the WCDMA physical data channels. In CDMA, which is a non-orthogonal multiple access scheme, the signals from different users within the same cell interfere with one another. This type of interference is known as the intra-cell interference. In addition, the base station also receives the interference from the users transmitting in neighbouring cells. This is known as the inter-cell interference.

Uplink power control is typically intended to control the received signal power from the active user equipments (UEs) to the base as well as the rise-over-thermal (RoT), which is a measure of the total interference (intra- and inter-cell) relative to the thermal noise. In systems such as HSUPA, fast power control is required due to the fast fluctuation in multi-user (intra-cell) interference. This fast fluctuation will otherwise result in the well-known near-far problem. Moreover, as uplink transmission in an HSUPA system is not orthogonal, the signal from each transmitting UE is subject to interference from another transmitting UE. If the signal strength of UEs varies substantially, a stronger UE (for example, a UE in favourable channel conditions experiencing a power boost due to constructive short term channel fading such as Rayleigh fading) may completely overwhelm the signal of a weaker UE (with signal experiencing attenuation due to short term fading). To mitigate this problem, fast power control has been considered previously in the art where fast power control commands are transmitted from a base station to each UE to set the power of uplink transmission.

When an orthogonal multiple access scheme such as Single-Carrier Frequency Division Multiple Access (SC-FDMA), which includes interleaved and localized Frequency Division Multiple Access (FDMA) or Orthogonal Frequency Division Multiple Access (OFDMA), is used, multi-user interference is not present for low mobility and small for moderate mobility. This is the case for the next generation UMTS i.e. LTE system. LTE system employs SC-FDMA in uplink and OFDMA in downlink. As a result in the case of LTE, the fluctuation in the total interference only comes from inter-cell interference and thermal noise which tends to be slower. While fast power control can be utilized, it can be argued that its advantage is minimal. Hence, only slow power control is needed for orthogonal multiple access schemes.

Nokia's Point, Click, Find

Nokia launches beta of 'Point & Find' system for mobile phones, letting consumers scan images for search with their camera phone.

The service can currently be downloaded in the US and the UK, on selected handsets. The phones supported by the current beta are the Nokia N82, N95, E66, N81, N76, E51, 6290, 6124 Classic, 6121 Classic, 6110 Navigator, and the 5700 Xpress Music.

Nokia has launched a beta of its new Point & Find system, which lets mobile phone users search for information on an object by looking at it with their handset camera.

Philipp Schloter, Nokia’s general manager for Point & Find, explained: "Simply by pointing their camera phone at a poster for a new movie, people can watch the trailer, read reviews, and find the closest cinema where it is playing.”

Other uses suggested by Nokia include scanning barcodes for prices, looking at items for sale and being sent more details on where to shop or coupons, or eyeing objects in a museum and being sent multimedia information about it.

The open platform system uses the camera to look at images, GPS positioning to decide where it is, and the internet to search though a database of tagged objects. When an image is recognised, links to content – such as film times or prices – are sent back to the user.

Nokia doesn’t just want consumer feedback, but is looking to hear from businesses about their ideas for the tech – click here for the Point & Find business site. It’s already being used by the Body Worlds exhibition at the O2 in London, so pointing the camera of a Point & Find phone at related advertising should bring up data on the show.

Sonim XP1: The toughest phone

This is billed as the toughest phone ever built:

• Water/Humidity: Impervious to the Wettest Weather
• Temperature Range: Works Perfectly In Extreme Conditions (-20C to +60C )
• Shock and Vibration: Drop It, Abuse It, Drive Over It – No Problem! The XP1 is Virtually Indestructible
• Screen: Unique No-Glare Coating Resists Scratches and Smudges
• Durable Case: Hardened Rubber Molding Cast Via Dual Injection
• Durable Mechanics: Keypad Buttons Tested To 500,000 Pushes Dedicated PPT Buttons Tested To 200,000 Pushes
• Dirt and Dust: Non-Porous Casing Blocks Entry of Micro-Particles

Comes with 3 years guarantee

Selling in UK for £249.00

Official website here.

Nokia favours LTE by dismissing WiMax

In the past few days the argument between WiMax and LTE camp has intensified. Both the camps are grabbing every single opportunity to pass disparaging remarks over the other. Evidently both WiMax and LTE are trying to be 4G bearer and in order to do so they are just pushing things to the limit.

It’s very well known that Nokia although has chosen LTE as their 4G technology, are still part of WiMax forum.

However what is astonishing is that Nokia has now strongly come out openly to dismiss WiMax as a 4G technology. This latest development will no doubt will generate some intensifying and interesting comments from both the camps.

Nokia by dismissing WiMAX as a 4G technology standard seemed to have solidified its support for Long Term Evolution (LTE) technology while comparing WiMAX's future to that of Betamax, the video format that met its demise when VHS triumphed in the 1970s and 1980s. In a recent Nokia launch event in San Francisco Anssi Vanjoki, Nokia's head of sales and manufacturing said the following:
"I don't see that WiMAX is taking hold anywhere in a big way. I don't think the future is very promising for WiMAX. This is a classic example of industry standards clashing, and somebody comes out as the winner and somebody has to lose. Betamax was there for a long time, but VHS dominated the market. I see exactly the same thing happening here."

The words above are really strong as far as dismissing WiMax as a 4G technology is concerned.

Nokia has wavered in its support for WiMAX in the past, but this is by far the strongest condemnation the world's largest handset maker has made of the technology. Nokia quite rightly present WiMAX's lack of backwards compatibility as one of the reasons why they think LTE is the future and for that very reason call WiMAX a niche play.

However it still remains to be seen whether Nokia is completely abandoning WiMax as it is still involved in WiMAX business development efforts.

Albeit it is still an immense argument as what will be 4G. Clearly from the dominant mobility operator perspective the trend is towards LTE. Any technology that gets rolled out has to provide global backwards compatibility because networks don't appear overnight. The only technology that offers you backward compatibility to CDMA and TD-CDMA and wideband-CDMA is LTE. It makes a huge difference because you're not building greenfield networks; these are evolutions of existing networks and the user experience has to be maintained. From that perspective, WiMAX doesn't quite have the same capability.

I don’t want to sound too harsh on WiMax and I think there might be a place for WiMAX as a fourth generation niche technology but I believe over time, LTE will be the standard bearer for 4G globally. The (WiMAX) technology itself, there's nothing wrong with it; it's strong and it ultimately will work. The question is whether there will be a market.

More on ICE

Continuing from the earlier post on ICE, Martin Sauter has some more information on this topic:

During the Mobile World Congress in Barcelona this year, I heard from Adrian Scrase for the first time that 3GPP has specified how to put information on the SIM card for "In Case of Emergency" (ICE) events, i.e. to help first responders to identify someone and to contact their next of kin.

A great idea and now that it is specified it will hopefully become a worldwide accepted feature. It's not in current phones and SIM cards yet so it will take a couple of years for the feature to be added. Let's keep our fingers crossed a critical mass is reached so people actually enter information and first responders actually use the feature.

As somebody asked me over at Forum Oxford at how it will work in practice, I've had a look at the standards:

• The user enters ICE information like names of persons, relation to these persons and phone numbers. For details see 3GPP TS 22.101, A28
• During an emergency, the information can be retrieved by pressing '* * *'. That's specified in 3GPP TS 22.030, 6.8
• The information is stored in a new file on the SIM card referred to as EF(ICE_DN) and the format is described in 3GPP TS 31.102

Fundamental difference between HSDPA and HSUPA

It has been long time since HSDPA and HSUPA came into existence. Untill now we have read and implemented many features related to HSDPA and HSUPA. However following are the basic difference between HSDPA and HSUPA:

• In the downlink, the shared resource is transmission power and the code space, both of which are located in one central node, the NodeB. In the uplink, the shared resource is the amount of allowed uplink interference, which depends on the transmission power of multiple distributed nodes, the UEs.
• The scheduler and the transmission buffers are located in the same node in the downlink, while in the uplink the scheduler is located in the NodeB while the data buffers are distributed in the UEs. Hence, the UEs need to signal buffer status information to the scheduler.
• The WCDMA uplink, also with Enhanced Uplink, is inherently non-orthogonal, and subject to interference between uplink transmissions within the same cell. This is in contrast to the downlink, where different transmitted channels are orthogonal. Fast power control is therefore essential for the uplink to handle the near-far problem. The E-DCH is transmitted with a power offset relative to the power-controlled uplink control channel and by adjusting the maximum allowed power offset, the scheduler can control the E-DCH data rate. This is in contrast to HSDPA, where a (more or less) constant transmission power with rate adaptation is used.
• Soft handover is supported by the E-DCH. Receiving data from a terminal in multiple cells is fundamentally beneficial as it provides diversity, while transmission from multiple cells in case of HSDPA is cumbersome and with questionable benefits as discussed in the previous chapter. Soft handover also implies power control by multiple cells, which is necessary to limit the amount of interference generated in neighbouring cells and to maintain backward compatibility and coexistence with UE not using the E-DCH for data transmission.
• In the downlink, higher-order modulation, which trades power efficiency for bandwidth efficiency, is useful to provide high data rates in some situations, for example when the scheduler has assigned a small number of channelization codes for a transmission but the amount of available transmission power is relatively high. The situation in the uplink is different; there is no need to share channelization codes between users and the channel coding rates are therefore typically lower than for the downlink. Hence, unlike the downlink, higher order modulation is less useful in the uplink macro-cells and therefore not part of the first release of enhanced uplink.

Femtocells in India: No thank you.

So many people ask me if Femtocells will be big in India but I am not sure if I know the answer to that. Honestly I will be surprised if any Indian operators have any plan of Femtocells and even if they are rolled out people might not be tempted.

In a post last month, David Chambers gave an interesting overview of facts and statistics of mobile and internet users in India:

First some details on the current situation in India:

- Population: 1.1 Billion

- 80% live in rural areas and survive on agriculture

- 39% are illiterate

- 27% live below the poverty line

- 77% live on less than US$0.50 per day

- The economy is growing at around 8-9% annually (and has done so for a few years), similar to China, but is still far behind in infrastructure – traffic congestion is throttling and there is not yet a metro/underground in the main cities, although some are being built.

- 2% PC penetration

And from a mobile phone perspective:

- It’s all 2G. No 3G licences have yet been awarded.

- It’s GSM. Both the CDMA technology operators (Reliance and Tata) who have a combined share of around 20% are said to be planning GSM technology rollouts, because the technology is cheaper and there is a wider range of handsets.

- It’s growing faster than anywhere else. Over 9 million new subscribers every month, with around 180million subscribers reported today. That’s still a huge growth to catch up with China, which has almost 500M subscribers, increasing by some 4M/month.

- Around 200,000 towers, with around 20% of towers hosting more than one operator’s basestation equipment.

- ARPU figures vary, with a lot of the newer subscribers probably in the US$ 2-4/month bracket, although overall the industry makes around $8/month

- Call rates are in the order of US 2 cent/minute.

- Yankee reports operator share of Bharti 30%, BSNL 18%, Reliance 17%. Vodafone (formerly Hutch) is growing quickly.

- 2G cellular data cards, using fixed price data plans, are becoming popular in a similar way to 3G cards/USB dongles promoted in developed countries. The data rates and capacity are more limited.

Yet from a wired broadband internet position:

- 3 million broadband DSL subscriptions

- 8 million copper loops capable of delivering broadband.

- 10 million dialup internet users.- Fibre is being laid across the country, but fibre-cuts remain a regular fault

So if we look at the potential for 3G femtocells, we find there is little comfort:

- No 3G licences available yet – this is probably some years off, whilst the country focuses on basic 2G voice/text rollout.

- Virtually no wired broadband to support significant volumes.

- Any 2G femtocells would likely conflict with the tight spectrum reuse and frequency planning of the macro network, so would be discouraged except where deployed and managed directly by the operator in extremely high capacity locations.

- The business case for coverage fill-in doesn’t stack up – broadband is unavailable in areas which don’t have cellular coverage.

- The business case for data in the home is even more difficult, with relatively low levels of domestic computer penetration. There is more likely demand for mobile broadband access via macrocells, using the new HSPA, HSPA+ and LTE technologies when 3G spectrum is made available.

So it’s not a question of deployment of 3G femtocells in the Indian market coming a few years after the developed world. The complete lack of copper loops, and the changing technology that makes it more feasible to deploy wireless broadband than dig up and lay new copper loops. The services that femtocells would offer are therefore more likely to be delivered over the macrocellular network (with microcellular support) in the medium and long term for any developing country. There is some interest in 2G picocells which would be deployed by the operator in enterprise situations to handle high traffic concentrations, but this is a different application, technology and market segment from the 3G proposition.

A similar view is reflected in this article here:

Bharti Airtel, Reliance Communications and Vodafone, all became members of Femtoforum about two years back but don't have any deployment of femtocell in the country. Femtoforum is a not-for-profit membership organization founded in 2007 to promote femtocell deployment worldwide. According to some media reports Bharti Airtel is conducting pilot projects for femtocells. The same is true for Reliance Communications and Vodafone, both are members of Femtoforum but are doing nothing about femtocell deployment in the country. Despite repeated attempts none of the service provider is forthcoming about femtocells deployment status.

In my recent visit to India I found that people have a different perspective of mobiles. For instance people couldnt understand why we use SMS so frequently and as a medium for communication (between friends, couples). India may probably have lowest tariff for voice and that is one of the reasons people use mobiles for. Many people have removed their landlines and use mobiles only, for their calls. Another most common use of the mobiles is to be reachable wherever you are. People havent learnt to switch their phones of silent and hence many places of worship in India are installing Jammers to stop mobiles working while you are thinking about God.

Similarly, people are not too bothered about the internet. They would generally use it on the weekends to write to their, friends, etc. If there is free net available in the office then its a different thing. The net speeds are also not very good and the link is not too reliable. One of the most popular application is Skype follwed by chatting applications.

I met many people who had Iphones or latest Nokia's/Samsung's but when I asked them if they did any data usage on their phones they all drew blank. I found one guy very actively using net on his E71 but he was connected via WiFi.

In this kind of situation, Femtocells may not be of much use to people. Femtocells would be useful as voice boosters but would that justify its cost. I dont think so. The main reason for surge in Mobile takeup is because its very cheap to make calls. You get some very good call bundles at really low cost. There are off peak rates which is 1/5th the normal rate. If the reception of a network is not good in somebody's house, he would change to a different network. In fact even now Mobile Number Portability is not available in India. As a result some people change mobile numbers every year.

With all these things in mind, Femtocells would be hard sell in India.

Coin operated 'Credit Crunch Mobile'

Bizarre concept, but I have already started liking it.

The following is from dialaphone website:

Following our brief earlier coverage of the phone set to challenge the Credit Crunch, we’re very excited to have the first artist’s impression of this new handset, codenamed the 100-F from a Latvian manufacturer, new to the mobile phone market, called Lirpa. It seems bizarre, but the phone design has been inspired by the global credit crunch (which must have reached Latvia too), and works as either a coin-operated or credit/debit card mobile. The UK variant will have a £1 coin slot for calls and a 10p slot for texts (not a bad price for a PAYG text) as well as a card slot (for which you’ll need to enter your PIN). It sounds like it will be quite bulky, maybe comparable with some of the smartphones around, and features will be limited - no camera or MP3 player as the components would take up too much valuable coin space.

Here are some of the 100-F features:
Colour screen - No
Bluetooth - No
Weight - 110g empty, 400g full
Available colours - Midnight Black, Dirty Grey and Grey Black
Card slot - Visa, Mastercard, Electron
Messaging - SMS, MMS, IOU
Ringtones - Built-in, Vibrate, Jangle

The idea behind this phone is obviously to make you think about how much you spend on calls, and we understand there’s another twist on this - users will be able to opt for having no access to the coin box, in which case they will have to take the phone to one of their network provider’s shops to have it emptied. None of the UK networks have commented on this as yet.

Dont forget to checkout the pre-order offers here.

Prisoners need mobiles too :)

Looks like there is a worldwide problem of Mobiles in the jails. Nearly everywhere mobiles are illegal in jails but people somehow manage to sneak them in.

First, this news from India about an inmate found with a mobile inside the prison. Apparently these phones are used by inmates to create co-ordinated attacks, etc. Sneaking a mobile in India is probably not too difficult because you bribe the policeman and he will get one for you ;)

In Brazil, it difficult to probably get a phone by bribing the policemen. That is why the prisoners have to ask someone to send mobiles using pigeons as carriers. Pigeons are carrying parts of mobiles which are being used by the inmates to assemble and create working mobiles. Maybe they can fix my old Nokia 6280 as well. Unfortunately couple of pigeons were recently caught and thats how authorities found out about them.

The Australian authorities in New South Wales have already passed a law stating that if someone is found smuggling mobiles in prison then they will face 2 years jail and $2200 fine. They are training dogs to sniff out mobiles.

In India a member of public (normal human being like most of us) has demanded that 'rude' mobile users should go to prison:

A petition filed by Gurjit Singh, a member of the public, demands that carrying mobiles at funerals and temples should be made illegal and the installation of mobile phone jammers on school buildings to block students from making calls mandatory.

Mr Singh also wants phone companies to roll-out apparatus would disable mobiles on the roads to avoid traffic accidents, and a law under which civil servants could be imprisoned if they make personal calls on their handsets during office hours.

His final demand is that mobile phones fitted with cameras be outlawed “for the safety of women”.

The measures may appear extreme, but have already won significant backing, including from The Times of India, the country’s most-read English language newspaper. “Mobile phones have made us less considerate for each other,” it said.

The newspaper went on to admit – somewhat ruefully – that banning mobile phones outright was not an option, but added: “The problem will only get worse, unless the parliamentary panel’s observations are taken seriously.”

India’s mobile phone market is one of the few corners of the global economy to have remained impervious – so far – to the effects of the credit crunch. In January, the country added a record 15 million subscribers, making it the world’s fastest growing, with customers from the country's poor rural areas driving the surge.

The industry's success has a dark side, however: in cinema theatres across India audience members can often be heard chatting on their new handsets, discussing the plot of the film as it unfolds on screen.

While even doctors commonly answer calls while treating patients.

The problem is made worse as the phone companies force as many conversations as possible through a limited amount of infrastructure, a cost-cutting measure that executives privately admit lessens the clarity of calls and means users often have to shout to make themselves heard.

There are, however, doubts over whether tough new penalties would work, especially when laws banning other public nuisances such as spitting have failed. A spokesman for RCom, India’s fastest growing mobile provider, insisted that while the industry takes the etiquette issue seriously there is a limit to what it can do. “This is really a matter of personal responsibility,” he said.

My solution for the Indian government is that mobiles should be allowed only in prisons :-)

ICE: In case of emergency

In case of emergency (ICE) is a program that enables first responders, such as paramedics, firefighters, and police officers, to identify victims and contact their next of kin to obtain important medical information. The program was conceived in the mid-2000s and promoted by British paramedic Bob Brotchie in May 2005. It encourages people to enter emergency contacts in their cell phone address book under the name "ICE". Alternately, a person can list multiple emergency contacts as "ICE1", "ICE2", etc. The popularity of the program has spread across Europe and Australia, and has started to grow into North America.