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'.

Microscope in your Mobile

Hair and Skin photographed with a mobile phone

Picked this up from Tomi via Forum Oxford:

Steve Litchfield of All About Symbian has coined the term 'Megapixel Microscopy', which is the process of using a high resolution cameraphone, in its native photography mode, to take pictures of tiny items, then to use the normal 100% size display on the cameraphone, as effectively a strong magnifying glass (or conversely a low-power microscope) to magnify the item.

Steve has some more interesting images on his website here.

Patent leaders of 2008

Interesting post in rediff about top 10 patent leaders of 2008:

1. IBM: It has become the first company to earn more than 4,000 US patents in a single year. IBM plans to increase by 50 per cent the number of technical inventions it publishes annually instead of seeking patent protection. This will make these inventions freely available to others. IBM, which earns about $1 billion annually from Intellectual Property, owned 3,125 patents in 2007. It now has a total of 40,000 patents.
2. Samsung: ranked second in the world in terms of patents. It comes close to IBM with a total of 3,515 patents
3. Canon: with over two thousand patents comes third in the list. It received 2,114 patents in 2008. Canon has established itself as a technology leader as it continues to be among the top five companies awarded US patents every year.
4. Microsoft: ranked 4th in the list of patent leaders. It won 2,030 patents in 2008
   Microsoft has been criticised for applying for patents of pre-existing technologies.
5. Intel: with 1,776 patents is ranked fifth in 2008.
6. Panasonic: Matsushita now known as Panasonic Corp comes sixth in the list with 1,745 patents. Panasonic's vision is to build products 'in harmony with the environment'. Panasonic makes products that can be easily used by people with disabilities also.
7. Toshiba: Toshiba is ranked seventh with 1,609 patents.
8. Fujitsu: with 1,494 patents is ranked 8th in the list.
9. Sony: Sony is ranked 9th in the world top patent leaders' list. It received 1,485 patents in 2008. However, Sony expects biggest-ever operating loss of $2.9 billion as the global economic crisis has led to a fall in demand for televisions, cameras and video game consoles.
10. HP: Hewlett-Packard is ranked 10th in the list of top patent holders. HP received 1,424 patents in 2008.

Intersting to see one South Korean and four Japanese companies among the top 10 list. Its just matter of time before some Chinese and Indian companies will break through the list.

Battle for ebooks on mobiles heating up

It seems that the new mantra for this month maybe 'ebooks on mobiles'. First the mobile operator '3' launched its ebook service. To be honest they have audio books as well as e-books. The only problem IMHO is the pricing which is between £5 and £10 for the complete book. There is also a possibility to download extracts for £1. Generally people in UK who want to read extracts, read them at the newsagents or bookshops for free during their Lunch time so I will be amazed if this service proves popular.

Amazon has said that books that Amazon.com Inc. sells for its Kindle electronic reading device will also be available on cell phones, too. Amazon spokesman Drew Herdener said Friday that the Seattle-based online retailer is working on making Kindle books available "on a range of mobile phones." The company is not yet saying when the books will be available, or on which phones.

Another e-book provider, Mobipocket, which is owned by Amazon, already sells titles that can be read on numerous smart phones.

Google has launched its Book Search service for mobile phones, featuring novels by Charles Dickens and Arthur Conan Doyle, as a challenger to Amazon's Kindle device. The internet giant has made the original text of 1.5m books available to be accessed for free via iPhone or Android phones. A spokesman for Google's book search mobile team said, "We believe we've taken an important step towards more universal access to books."

Experts said they expected an online battle for the market. Stuart Miles, of gadget website Pocket Lint, said: "Google has obviously seen how Amazon dominated the online selling of real books, and wants to stop that happening again. By offering free, out-of-copyright books they can instantly offer this huge library.

"Google's approach is also very clever because it is costing them very little, as they don't have to develop their own hardware."

Of course you can always download books on your windows devices and they can be read via PDF readers ;)

Indigo Books & Music Inc. believes strongly that the market for e-books is hitting critical mass, and, most important, that consumers will want to read e-books anytime, anywhere. Which is why the multi-channel retailer next month will launch Shortcovers, a mobile and conventional web destination for free and paid electronic content ranging from books and magazines to newspapers and blogs.

Shortcovers, Indigo Books & Music tells Internet Retailer, is a new division of the company with its own e-commerce infrastructure. Shortcovers in February will launch its web site and a mobile application for the iPhone. IPhone users can download the free program in Apple’s App Store. They create an account and profile through the mobile app or at Shortcovers.com that will enable them to search, browse and download e-books in numerous file formats, most significantly the publishing industry’s ePub standard. Indigo will introduce mobile applications for smartphones using the BlackBerry, Android and Symbian mobile operating systems, in that order, but did not specify a timeline.

MIMO schemes in LTE

SU-MIMO (Single User MIMO)

•This is an example of downlink 2x2 single user MIMO with precoding.

•Two data streams are mixed (precoded) to best match the channel conditions.

•The receiver reconstructs the original streams resulting in increased single-user data rates and corresponding increase in cell capacity.

•2x2 SU-MIMO is mandatory for the downlink and optional for the uplink

MU-MIMO (Multiuser MIMO)

•Example of uplink 2x2 MU-MIMO.

•In multiple user MIMO the data streams come from different UE.

•There is no possibility to do precoding since the UE are not connected but the wider TX antenna spacing gives better de-correlation in the channel.

•Cell capacity increases but not the single user data rate.

•The key advantage of MU-MIMO over SU-MIMO is that the cell capacity increase can be had without the increased cost and battery drain of two UE transmitters.

•MU-MIMO is more complicated to schedule than SU-MIMO

100% secure Zumba Lumba Phone to be available soon

Its a really catchy name and I may just buy it because of the name ;)

Rather than being developed by one of the world's large, well known handset manufacturers, the Zumba is being developed by IA Technologies, based in Hereford in the UK, using the brand name, Zumba Lumba.

It is being touted as potentially revolutionising the industry, due to what its makers claim is the world’s most accurate voice recognition system.

The Zumbafone could be available by the end of this year, according to reports.

The innovation is a circular pad that can be placed over the ear and detaches from a small handset that contains a circular dial pad and screen. Simply removing the earpiece pad from the handset activates a connection to the internet. You then simply say the name of a contact to dial a number or send a text. When you receive a text it can them be read out to you.

No contact information is stored on the handset itself, with all data being held ‘in the cloud’, which the makers say makes the phone 100 per cent secure. As it is fully tied to voice recognition, the claim is that if lost, the phone cannot be used by anyone else.

The phone is aimed as a low cost, or secondary phone, so eschews features such as high resolution screen and camera.

What is Zumba?

Low cost, simple and a refreshing new way to communicate

Unlike any other mobile phone or phone service

Designed and developed to become a real and exciting alternative

An everyday phone, or simply a back-up phone, Zumba strips away the complexity and expense of heavily featured handsets and introduces a fresh new way of making calls. Zumba does away with the need to remember phone numbers - you simply say your contact’s name and Zumba will connect you.

Because the Zumbafone is so exceptionally light and small it can be worn. As you can see from the pictures, it has a detachable keypad and screen which means you can wear it by slipping it over your ear.

Zumba has already been in development for three years and is in the final stages of development this year. We are looking forward to bringing our service to market and making its many benefits available to all.


You can watch Youtube video of ZumbaLumba:

GSM: Architecture, Protocols and Services

There is a new book on GSM in the market. Now it makes me wonder that since we are all focussing on 3.6G, 3.75G, 3.9G, 4G, etc., etc. what would be the point of a GSM book?

The following is from the preface of the book:

The GSM family (GSM, GPRS, EDGE) has become one of the most successful technical innovations in history. As of June 2008, more than 2.9 billion subscribers were using GSM, corresponding to a market share of more than 81%, and its story continues, even now, despite the introduction and development of next-generation systems such as IMT-2000 or UMTS (3G) and even systems beyond 3G, dubbed IMT-Advanced.

At the same time, wireless local area networks have substantially expanded the wireless market, sometimes drawing market share from GPRS and 3G (e.g. in public WiFi hotspots), sometimes coexisting (e.g. in UMTS home routers used as a replacement for fixed wire connections). However, these are used typically for low mobility applications. Mobile communication with all of its features and stability has become increasingly important: cellular and GSM technology, plus, of course, lately 3G, GSMs sister technology, so-to-say.

Another impressive trend has emerged since our last edition: the permanent evolution in the handheld market, producing fancy mobile phones with cameras, large memory, MP3 players, Email clients and even satellite navigation. These features enable numerous nonvoice or multimedia applications, from which, of course, only a subset is or will be successful on the market.

In this third edition, we concentrate again on the architecture, protocols and operation of the GSM network and outline and explain the innovations introduced in recent years. The main novelties in this book are the presentation of capacity enhancement methods such as sectorization, the application of adaptive antennas for Spatial Filtering for Interference Reduction (SFIR) and Space Division Multiple Access (SDMA), a detailed introduction to HSCSD and EDGE for higher data rates, and an update of the available GSM services, specifically introducing the Multimedia Messaging Service (MMS).

I think that GSM is going to be the fallback option for most of the new technologies due to its worldwide deployment so now is the time for us to brush up our GSM concepts

Advances in Underwater Wireless Communications

The IEEE Communications Magazine, January 2009, has a interesting section on Underwater Wireless Communications for those who may be interested.

Underwater networks of sensors have the potential to enable unexplored applications and to enhance our ability to observe and predict the ocean. Unmanned or Autonomous Underwater Vehicles (UUVs, AUVs), equipped with underwater sensors, are also envisioned to find application in exploration of natural undersea resources and gathering of scientific data in collaborative monitoring missions. These potential applications will be made viable by enabling communications among underwater devices. UnderWater Acoustic Sensor Networks (UW-ASNs) will consist of sensors and vehicles deployed underwater and networked via acoustic links to perform collaborative monitoring tasks.

The single most killer application for Underwater Wireless Communication would be in disaster prevention. Sensor networks that measure seismic activity from remote locations can provide tsunami warnings to coastal areas, or study the effects of submarine earthquakes (seaquakes).

There are major challenges in the design of underwater acoustic networks that include:

• The available bandwidth is severely limited;
• The underwater channel is impaired because of multipath and fading;
• Propagation delay is five orders of magnitude higher than in Radio Frequency (RF) terrestrial channels, and variable;
• High bit error rates and temporary losses of connectivity (shadow zones) can be experienced;
• Underwater sensors are characterized by high cost because of a small relative number of suppliers (i.e., not much economy of scale);
• Battery power is limited and usually batteries cannot be recharged;
• Underwater sensors are prone to failures because of fouling and corrosion.

There has been intensive research on MAC protocols for ad hoc and wireless terrestrial sensor networks in the last decade. However, due to the different nature of the underwater environment and applications, existing terrestrial MAC solutions are unsuitable for this environment. In fact, channel access control in UW-ASNs poses additional challenges due to the peculiarities of the underwater channel, in particular limited bandwidth, very high and variable propagation delays, high bit error rates, temporary losses of connectivity, channel asymmetry, and extensive time-varying multipath and fading phenomena. Existing MAC solutions are mainly focused on Carrier Sense Multiple Access (CSMA) or Code Division Multiple Access (CDMA). This is because Frequency Division Multiple Access (FDMA) is not suitable for UW-ASN due to the narrow bandwidth in UW-A channels and the vulnerability of limited band systems to fading and multipath. Moreover, Time Division Multiple Access (TDMA) shows a limited bandwidth efficiency because of the long time guards required in the UW-A channel. Furthermore, the variable delay makes it very challenging to realize a precise synchronization, with a common timing reference.

The next challenge is to select a routing protocol from a range of protocols that will work in the best manner with the MAC solution selected.

Another challenge is to select the correct transport layer protocols. A transport-layer protocol is required to achievereliable transport of event features and to perform flow and congestion control. Most existing Transport Control Protocol (TCP) implementations are unsuited for the underwater environment because the flow control functionality relies on window-based mechanisms that require an accurate estimate of the round trip time (RTT).

If you dont have access to IEEE Comms Mag then you can still read one of the papers online here.

Story of two Femto's from opposite end of the world

Verizon (USA) wireless introduced a femtocell product officially and have called it as "mini-cell site". Made by Samsung this will retail at $250+. The big advantage with this is that the phone calls that originate/terminate on "mini-cell site" would be free. The big problem is that this cell only serves voice but not data. So no faster data or any enhanced data services on this one. Maybe that is in the pipeline...

On the other side of the world, in Singapore, Starhub had launched the first "commercial" femtocell service called "Home-zone" back in Nov. It has received positive review in Telecom TV Wireless 3.0 article.

All I had to provide in advance was provide my cable modem MAC address and the phone numbers of the mobiles that would be used in the house (up to four). As soon as theHuaWei femtocell was connected it was recognised by the network it immediately took over from the nearest base station (about 300 metres away) by ‘shaking hands’ with the two mobile phones in our house.

The only noticeable difference was that my handset (a 3GiPhone) showed the StarHub network name and unique cell number. My wife’s phone (an HTC running Windows Mobile) thought it was roaming and only displayed the symbol for that function. I am told that newer Nokia phones actually state they are connected to a Home Zone service. Presumably, as femtocells become more common there will be a standard way of indicating connection. This notification is pretty important as I will explain later.

Previously on one side of the house I had good service to the network, on the other almost none. I found it quite clever that as I walked outside through the doors on either side of the property, the connection switched to the main network. I doubt if this was planned and was most likely coincidental, but it continues to amaze me how clever it is to do that. If the signal was much stronger then the Home Zone service could be subject to abuse. Apart from the differences mentioned above, and just in case I don’t notice the cell ID on my handset, as a call is made a comforting voice lets me know that I am making the call from my Home Zone. I thought this might become annoying but it is comforting to know that I’m connecting via the femtocell and saving my valuable package minutes.

In fact, all calls made from my fixed line (via cable) service, are also free but as my mobile plan comes with a number of free minutes and SMSs included each month, these are not decremented when I connect via the femtocell. Of course, the international segment of my calls are NOT provided free! I spent some time chatting with StarHub’s billing specialists to see how they handled my femtocell or Home Zone calls.

As expected, each call had a unique femtocell identifier and this determined how the call would be handled in the billing system.

It also allows for some creative plans and billing by operators hoping to capture extra market share using femtocell technology.

By the way, if a call is instigated on the Home Zone network and I move outside of the femtocell's range, the call is handed off to the main network but continues to be zero rated. A nice feature I thought. However, calls started on the main network are NOT handed off to thefemtocell, if you happen to already be on a call as you arrive home. That would create quite an interesting billing scenario I suspect.

So, what’s in it for the service provider? Firstly, I am charged a nominal fee of SG$16 (US$11) per month for the use of the femtocell and I suspect that this covers the cost of the unit I was provided with. Considering that I have two digital home services over the cable network also offered by StarHub (a free service if you are also a cable TV customer), then why would I want to pay for the new access method?

Well, I guess I won’t need those two other phone lines any more and will, like many others, use my mobile number as my primary and only contact point in the future. So StarHub loses two lines that earn them no revenue and I get the same free service via my mobile phone and we both win.

Where this does make a big difference is that customers of StarHub’s main competitor, SingTel, who still pay a monthly subscription for their dial up service, may be tempted to swap to StarHub and get the same service via their mobile phone. There will be thousands of permutations of how femtocells can be used for competitive advantage across all markets, but this is just one. This is as ‘sticky’ as it gets!

Of course, I am doing StarHub a great favour as well. If you consider that I pay for my broadband access and that all my home zone calls and data traffic go down that route, I have eased some burden on Starhub's wireless network. If enough people swap to femtocells this could provide a dramatic reduction in 3G/HSPA network traffic.

And when you consider that backhaul costs keep increasing this is great news for operators and should reduce the need for continuously expanding wireless infrastructure.And what about those customers who have poor or marginal coverage in their home or apartment? Femtocells are exactly what they need. As femtocell production numbers increase their cost will also drop and they may be given away free to high ARPU prospects and customers.

Like all new technologies, StarHub discovered some early glitches that have since been remedied. Enterprising early adopters worked out that they could take their femtocell with them and simply plug into a broadband ethernet port anywhere in the world and make calls to Singapore for free on their mobile phones! This has now been corrected and the femtocell must be connected directly to the StarHub network to be recognised.

Early femtocells also had difficulty with the hand-off to and from external cells and with automatically varying signal power as the handsets came closer to the femtocell. Working closely with the equipment vendor StarHub has ironed out most issues and the latest femtocells appear to be efficient and reliable.

Operators like StarHub see this technology as a complementary and an effective tool to attract and maintain customers ahead of their competitors. They also see femtocells as an avenue to push promotions and offers to customers over the air, and they may become quite a weapon in capturing key customers in one very tough market. If all their customers have the same experience as me, femtocells will be a big winner.

LTE Status: Jan 09 updates

According to this news, Verizon Wireless says that the Next-Gen 'LTE' Wireless Network Still On Track For 2010 Launch:

Despite a tanking economy and a potential delay getting access to the spectrum Verizon bought in last year's FCC auction, the telco says it's still on track to roll out its next-generation wireless network next year.

On the company's earnings call today, Verizon COO Denny Strigl said he's still hoping LTE will be commercially available in the first half of 2010, with in-house testing to begin later this year.

Meanwhile in Sweden, Swedish telecommunications operator TeliaSonera has signed contracts towards the launch of an 4G high-speed wireless network in 2010, saying it aims to be one of the first with an LTE network up and running.

TeliaSonera said on Thursday it had signed up Ericsson to construct its initial Stockholm LTE (the Long Term Evolution of 3G) network, and Huawei for the initial Oslo network. Both equipment makers said it was their first commercial LTE contract.

The telco said it is still evaluating suppliers for further LTE networks across Sweden and its other markets.