The Wireless Corner

I haven’t had much time to write lately since I am on vacation. I will be back with a lot of news in about 10 days..

However, I did see this title at tech.yahoo.com Why I’m Not Getting an iPhone and thought it’s worth the read. Speaking of the iPhone, today is June 29th, the big day! I haven’t heard anything new about it yet but I am looking forward to see what people have to say after they buy it..

I am connected right now to a Wi-Fi connection at an airport and it says its 11 Mbps. However, it doesn’t seem like it. Wi-Fi connections are suppose to be fast although some factors that effect the speed of the connection is the number of poeple using the network at the same time, the amount of downloads and the access point location.

Well I am adding to this post the next day. Yesterday while I was writing and trying to save what I wrote, I kept getting “internet page not found” page and also I was unable to publish it due to the same reason. I wonder why that happened, I didn’t have problems with the other sites I visited besides the connection being very slow. Why would a Wi-Fi connection say its on 11Mpbs and work as if it was 256 Kpbs? Far access point? Too many users?

In a previous post I talked about some of the ways to increase the performance of a cellular network so that you don’t get blocked or dropped calls (here). One of those ways was by using a multi-tier cellular network.

A multi-tier cellular network is a network that has different types of cells that overlay each other. Each type of cells differs from the other by the size. The smaller the size of the cells is in a certain area, the more channels can be available for users (since the number of channels are fixed for the cells). As you can see from the image below, there are 4 types of cells:

1. Picocells (radius 10- 50m) are used inside buildings and elevators. The cell antennas are placed in corners of the room or hallways and is used when the number of users in the building is high and signals from the outside cells cannot penetrate the building. (There is a new type that has almost the same features as picocells that is called Femtocells, I talked about it briefly here).
2. Microcells (radius 100m -1km) are cells used mainly in cities where there are alot of users.
3. Macrocells (radius 1km -20km) are used in rural areas since the number of users isn’t high and also in high populated areas where microcells are too small to handle the frequent handoffs of users that are mobile while making a call. For example, if you are in a high speed car and are connected to a microcell, what might happen is that the speed of the car is too fast for your call to be transfered (handed-off) from one base station (cell antenna) to another which will cause your call to be disconected. And that is not what we want, thats why macrocells are used for those types of users. And the network can sense the speed of the user, if the user is walking or in a high speed car, then the call is transferred to the appropriate cell accordingly (microcell or macrocell).
4. Satellite (world wide coverage).

Do all areas use all 4 types? Nope, it mainly depends on a couple of factors:

• Population: in high populated areas, cells with smaller radiuses are preferred to accomodate the high number of users.
• Geography: whether its a mountinous area, flat terrain or desert.
• Building structures and type: some buildings do not allow penetration of the cellular signal therefore picocells are used.

Having multi-tier cellular networks increases the number of cells, which means more users are able to use the network without being blocked and users in cars or any high speed vehicles are able to talk without worrying about their calls being disconnected.

Chris of Engadget talks about two new walkman phones by Sony Ericsson, the W910 and W960 here. 

W910 supports GSM, UMTS, GPRS, EGDE and HSDPA (HSDPA is considered a 3.5G network for high speed data rates). One of its new features that I found interesting was:

Perhaps the coolest feature, though, is “Shake control” — flick the phone to change tracks, shake it to randomize the playlist.

Meanwhile, the W960 has 8GB memory and supports Wi-Fi along with UMTS. You can find the press release and list of features for both phones on the Sony Ericsson web site here.

The iPhone is scheduled to hit the markets on June 29th. I am sure for those of you who follow up on the iPhone news have heard almost everything there is to know about it. I even read the other day about a poll that showed results about the gender, age group and location of the poeple who plan to buy it. Not a single phone has been sold yet and there are reviews everywhere (yea I know even me… though I had to comment).

That brings me to today, Ricky Cadden (the Symbian Guru) wrote a very interesting comparison between the iPhone and Nokia N91, which you can read here. I agree with the points he discussed especially the part about the good marketing stategies Apple has been using in the U.S. compared to Nokia. (Here in Europe, Nokia is one of the top sold phones and I don’t remember seeing a single advertisement about the iPhone yet and not even sure it’ll be sold on the 29th.. actually I just read that it won’t be here till the end of the year, not sure though). Another thing I found very interesting was the number of shops in the U.S. that sell Nokia phones compared to the ones that’ll sell the iPhone.

Well let’s see what the reviews will say when poeple actually start using it..

If you have been shopping recently for a new cell phone and wanted the latest technologies included then I am sure you came across cell phones that also support Wi-Fi.

Multi-Mode means that it can operate on different networks like GSM, UMTS and Wi-Fi (it has nothing to do with the frequencies, that would be called multi-band phones like a tri-band GSM 800/1800/1900MHz phone). When a cell phone supports Wi-Fi that means it can connect to the internet and use data services including VoIP.

Where do you use your cell phone the most? According to the type of job and the lifestyle that you have, that answer could vary. But let’s assume you work in a office that has a wireless network and you use your cell phone frequently to make deals with clients. Using the Wi-Fi supported cell phone you can make your call using VoIP. Then let’s say this important client has alot to say while you need to leave the office to go to another meeting. No problem, you don’t have to end the call since your cell phone will sense that you are about to leave a hotspot (signal starts to degrade) and so it makes the attempt to connect to the cellular network and something that is called “handoff” occurs (handoff is the process of moving from one cell to another, in this case moving from a Wi-Fi hotspot to a cellular network).

One of the multi-mode phones in the market is Nokia N80i (i stands for Internet). It operates on GSM, UMTS and Wi-Fi networks. Brian McConnell wrote on the O’Reilly Emerging Technology site his reviews and experiences with this phone which you can read here. One of the features I liked the most was the ability to select the name you want to call, choose Internet Call and you are immediatly connected, which is possible due to the SIP (Session Initiation Protocol) that is attached to the phone’s address book therefore, no additional VoIP client downloads are necessary.

I wonder if we’ll start to see poeple going to cafes and public places that have hotspots specifically to make phone calls? Hmmm.. I’ll do a little research on the impact of these phones on the cellular service providers. I am sure there is something in it for them too.

When you want to make a phone call with your cell phone, you enter or select the number you want to call and press “call”. After that you wait a while until you get a response, either with the other side ringing or with a message saying its either turned-off/busy. Other responses could be “the network is busy” or you just keep waiting to hear something while nothing comes up, so you try again.

When you can’t get through or the network is busy, one of the reasons is that there is no space in the cell for you to make a call. In more technical terms: there is no free channel to be allocated for your call. In a cellular network, the number of channels is fixed. Thats why there are several techniques to increase the effciency of a cell and allow more users to use the network.

I will talk about one of those techniques that is used in a GSM network. Each channel in a cell is divided into time slots and each time slot is assigned to one user. This access technique is called TDMA (Time Division Multiple Access). The user will not notice that during the call, the channel is actually being used by other users. This is because the time assigned for each slot is very short (~0.577 ms) . Think about the channel as a wheel that rotates. The user assigned to the first slot of the wheel will get to the use the channel after the wheel completes one rotation, and so on. 

Some of you now might be wondering, why is there a fixed number of channels in each cell since we are using the air which should be limitless. Well each network can only operate on a certain radio frequency (spectrum) and the service provider must buy the license to use it. This prevents interference with other services (such as. radio, TV, UMTS… etc.). I am sure all of you have noticed when buying a cell phone it includes the frequencies it can operate on, for example: GSM 800, 1800 and 1900 MHz. 

Well thats one way, another way to allow more users use the network is to make the cell size smaller and/or add another layer of cells on top of the existing one, in this case the network is called a multi-tier(layer) cellular network. I will talk about this in a next blog entry.

Remember the days where a phone was just a device you hooked up at home to make voice calls.. Yes, it was that simple.. Well now our phone (also called cell phone) does not need to be hooked up anywhere and does alot more than just allow us to make voice calls (you can read more about this in my previous post here).

Speaking of those old days, I came across an article at tech.msn.com about the history of cell phones (here), it shows how cell phones evolved from being the huge 2 pound phones to the elegent multi-feature phones that they are today.. I remember my first cell phone back in year 2000. It was a Motorola phone, black color with a basic design and a small green screen (I don’t remember the model). The only feature it had was SMS and I was pretty happy with it at the time..

I know its been a while since my last post.. But I will be back soon with the latest in the telecom world..