Femtocells

Femtocells are small cellular network used in homes, offices etc.

In the beginning, there were many debates and thoughts on femtocell:

• Is it really required?
• Will it be commercially successful?
• As femtocell will use the same frequency bandwidth as MACRO then how it deals the interference issue with MACRO.

Advantages of femtocell:

• It improves coverage. Generally, in the basement of the building or in the cell edge area, MACRO network coverage is not so good. In such places, femtocell creates it's own small cellular network and provides good network coverage.
• Being in high coverage area, UE requires less power to transmit and hence saves battery power which is very important in the world of smart phones where so many background services runs.
• Less deployment cost comparing MACRO deployment.
• Decreases the MACRO load. With more number of femtocells, the MACRO can serve more number of users at a given point of time.

Femtocells have it's own advantages from the both operators and users perspective. Consequently, many telecom biggies invested huge money to develop and deploy the femtocells and it's equally adopted by users happily in many countries.

Femtocell in future:

Being a home based cellular system, it can improve the home security, personal safety, and help integrating smart phones with other home appliances like TV, AC, Laptops, Media Players etc.

When children phone (registered users) comes in the coverage area of home femtocell, the parents can be informed by SMS. 

Also, they can be integrated for a registered user that which appliances need to ON when it's in the coverage of femtocell i.e when registers users phone latch on the home based femtocell network, it can automatically ON appliances like lights, AC etc.

But, it's not all rosy picture for femtocells in future. Femtocells have to compete with Wi-Fi networks.
To understand this, let's do comparative analysis of both the femtocells and Wi-Fi network.
Femtocell vs Wi-Fi

1. From the operators perspective, femtocells are more preferred as it's easy to integrate with the existing network whereas Wi-Fi has lesser inter-working with the existing network and there are concerns of handset choices etc.
2. Femtocells has additional cost of box over Wi-Fi and here Wi-Fi has advantage over femtocells.
3. Femtocells can only be used in its home location only whereas a Wi-Fi enabled phone can use any of the Wi-Fi network (access provided).

Hence, femtocells promotors have to work on idea and proposals so that additional cost of the box can be covered and also provides an attractive propositions for it's users.

Femtocell in INDIA:

With growing demand of high capacity and coverage and increase in the number of mobile users in India too, it's quite possible that we may see femtocell soon in India.
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HARQ Procedure

Automatic Repeat Request (ARQ) is a re-transmission protocol in which the receiver checks for errors in the received data and if an error is detected then the receiver discard the data and requests a re-transmission from the sender.
Hybrid ARQ (HARQ) is re-transmission protocol in which the receiver checks for errors in the received data and if an error is detected then the receiver buffers and requests a re-transmission from the sender. A HARQ receiver then combine the buffered data with the re-transmitted data prior to channel decoding and error detection. Hence, even if the re-transmitted data is partially received in error, after combining with buffered data may be error free and no further re-transmission required.
Parallel HARQ processes used to avoid impact on throughput. When one HARQ process waits for the ACK, the second HARQ process can transmit in subsequent TTI. These parallel processes are known as Stop and Wait processes because they stop and wait for ACK from the receiver before sending any further data.
3GPP allows maximum 8 parallel HARQ processes to be configured for an individual UE.

HARQ in HSDPA:

• The number of parallel HARQ processes at any point is dynamic and changes according to rate TTI are scheduled.
• It can use maximum of 8 processes.
• The HS-SCCH is used to inform the UE that which of the HARQ process is being used at any point of time. 

HARQ in HSUPA:

• The number of parallel HARQ processes are fixed. 
• A HSUPA connection using a 10 ms TTI always uses 4 parallel HARQ processes whereas a connection using 2 ms TTI always use 8 parallel HARQ processes.
• It is not required to inform NodeB that which HARQ process is used at any point of time. The HARQ processes are allocated to consecutive TTI in a cyclic fashion.

UTRAN Initiated Security Mode Procedure

In GSM, Integrity is not there. But in UMTS, Integrity is mandatory.

In case of Inter System Handover, when an UE comes from GSM to UMTS system, UTRAN should trigger the Security Mode Procedure to start integrity. This is solely UTRAN initiated procedure and not triggered by Core Network. The integrity key and algorithm used are the one which was received in Handover Request message. The Security Mode Command message should not include the ciphering info as this is to start integrity.

If ciphering was enabled on the GSM, then UE enabled ciphering immediately after receiving Handover To Utran Command message and consequently the next message Handover To Utran Complete sent by UE will be ciphered.

UMTS Introduction

UMTS stands for "Universal Mobile Telecommunications System".

The 3rd Generation Partnership Project (3GPP) has been responsible for generating the technical specifications which defines the UMTS protocols and performance requiremnts.

Based on time to time requirements from both Operators and Users, the technical specifications continue to evolve e.g. from only circuit switched call to normal packet switched call to hsdpa call to hsupa call and so on.

With increasing requirements like high data rate, high throughput, multiple services at a time, everyone talking and putting continuous efforts to achieve them.

UMTS high level architecture: