CELL_FACH to LTE reselection in 3GPP release 11

Just to keep everybody on their toes it seems the wise people at 3GPP decided to introduce mobility from 3G CELL_FACH to LTE from release 11 onwards. As the figure above shows (TS 36.331), that all important arrow from CELL_FACH to E-UTRA RRC_IDLE has been introduced. Why it was not included  in the first place is still a mystery to me as from a UE complexity point of view I wouldn't have thought it would be that difficult. From a RAN point of view it just re-uses the FACH measurement occasion concept defined since release 99 that allows a UE to search for inter frequency and IRAT neighbours during specific time intervals when it knows the RAN will not send it any data on the SCCPCH.

In addition to the above, SIB19 on 3G has some changes as the operator can choose if all EARFCNs will be searched for or only the higher priority ones (if applicable).

Although CELL_FACH can be thought of as a transient state it is possible that a UE can stay there long depending on RNC inactivity timers and keep alive periodicity from applications on the UE. With this change then the possibility of being "stuck" in 3G is minimised.

Base station in disguise, gone wrong..

One of issues faced with operators around the world is getting planning permission for base stations. At least here in the UK, one of the most common designs is the base station disguised as a lamp post. They usually blend in nicely, the public don't even notice them and some even have a functioning lamp so they serve a practical purpose besides housing an antenna.

Sometimes however things go wrong as the photograph above shows. I wonder how many people notice that it is a bit strange to have two lamp posts separated by 1 metre. Clearly the traditional lamp post should be removed but I guess someone got a bit lazy.. 

Small Cells, Big Impact (my version)

I was reading the now few month old announcement from AT&T around small cell strategy here and a few things came to mind. First, the story. AT&T announced back at the end of January that they were planning to roll-out 40,000 small cells by the end of 2015. They have also posted a video on the link above that shows one of the products they are trialing, which although the logo is purposefully out of focus can easily be identified as the Alcatel Lucent 9364 Metro Cell described here. The video also mentions that AT&Ts plan is to roll these out to improve coverage which is where an important distinction in my opinion has to be made.

Small cells can be used for two scenarios. Scenario 1: Not spot. Scenario 2: Hot spot.

Scenario 1 is the easier of the two and the one AT&T has opted for. Regardless of how much an operator can try some areas will always suffer from poor/no coverage. Once these areas are identified a small cell can easily be installed to provide coverage. Small cells due to their femto background are easily deployed, mostly auto-configure and require just a backhaul connection which can be of xDSL nature. Due to their small size they are also usually exempt from the usual painful planning permission process.

Scenario 2 is the more difficult one. Here there is macro coverage, but due to the high amount of traffic the macro network cannot cope. The solution? Either try to use Wi-Fi offload (with the problems described in my previous post here) or use a small cell to absorb some of the traffic. However placing a small cell among large powerful macro cells is not as easy as some people make. At best the range of the small cell is severely interference limited and at worst it acts as a noise source affecting macro network performance. In addition to this UE uplink power can interfere with the small cell when power controlled by a macro cell further away. The solution to these problems is the new industry buzz word "HetNets" (Heterogeneous Networks). But what does Heterogenous mean anyway?

heterogeneous [ˌhɛtərəʊˈdʒiːnɪəs]adj

1. composed of unrelated or differing parts or elements

2. not of the same kind or type

When it comes to mobile telecoms, HetNets is essentially an umbrela term to descibe a number of features (some standardised and some not) that allow nodes of different types (macro cells, small cells etc) to co-exist. To date most of it is theoretical or simulation based so it is too soon to draw any conclusions as to how well HetNets will perform.

Another thing to bear in mind is that HetNets require close co-operation between the small cell and the macro cells which is where the small cells from a femto background might face some problems due to their flat architecture (combined RNC/nodeB) which essentially makes interactions between small cell and macro cell inter-RNC based. Traditional macro cell vendors have recognised this opportunity, which is why most of them are introducing small cells in their product portfolio.

All is not lost though, as vendors from a femto background already have a lot of experience in interference mitigation techniques and also auto configuration which when dealing with a large number of cells is a strong requirement.

It also worth remembering that LTE is based on a flat architecture so any advantages traditional macro vendors have might be short lived.

So, it will be interesting to see which small cells are the eventual winners. Will it be the enhanced femto cells or the miniaturised macro cells?

Nokia 6150, thirteen years on

When I started working in the mobile telecoms industry back in 2000, my employer at the time gave me a Nokia 6150. It was my first mobile phone and I loved it. At the time Nokia was the dominant force in mobile handsets and the 6150 was regarded as a top end device. Apple on the other hand in 2000 was purely focused on computers, launching products such as the Power Mac G4 and the iBook.

As time passed I got other mobiles and sold off the Nokia 6150. A few days ago however in a fit of nostalgia I went on eBay and purchased another 6150. A couple of days later I had in my hands and the rubbery keys felt instantly familiar. As I powered it on to make that first call, it got me thinking how much things have changed in the past 13 years..

So let's see. The Nokia 6150 supports GSM. That is it. No GPRS, no EDGE, no 3G, no HSDPA, no HSUPA, no HSPA+. Life was simple back then. Just GSM. The 6150 was dual band so it supported GSM in the 900MHz (no E-GSM though) and  the 1800MHz band. This at the time was quite a revolution. It also supported SMS, but only to a maximum of 160 characters, no concatenation. For data, it supported CSD (Circuit Switched Data) which essentially was a dial-up modem at an amazing speed of 9.6kbps! From a codec perspective it suppoted Full Rate, Half Rate and Enhanced Full Rate. No AMR obviously. Looking further into its capabilities it also supports the A5/2 cipher algorithm which has since been removed as a ciphering option by the GSMA.

Fast forward 13 years and the mobile telecoms industry has completely changed. But GSM networks are still around and are still backwards compatible as my Nokia 6150 works perfectly. I guess this is testament to those people in ETSI who developed GSM.

Comparing the Nokia 6150 to my current mobile, an iPhone 4, is obviously an unfair comparison but one thing has not changed...

The weight. They both weigh 140gr!