How does a UE(mobile) detects the Scrambling code of the cell, when it is switched on?

When the UE(mobile phone) is switched on, it doesnot have any idea regarding the Primary scrambling code that is used in the cell and it is not having any synchronisation with the network.

Now lets have a look at how the UE gets the time slot synchronisation and learns about Primary Scrambling code of the Cell.

When the UE is switched on, initially it will be trying to attain time slot synchronisation. For that it will start listening to Primary Synchronisation Channel (P-SCH). The slot timing of the cell can be obtained by receiving the primary synchronization channel (P-SCH) and detecting peaks in the output of a filter that is matched to this universal synchronization code. This P-SCH is sent during the first 256 chips of every slot. the whole slot is 2560 chips long. Thus the UE can identify when a time slot starts, i.e by decoding the first 256 chips, but still the UE cannot determine the slot number and hence it doesn’t have an idea regarding the radio frame boundary also.In UMTS there are 15 time slots in each radio frame.Each radio frame is of 10ms duration.

Thereafter the UE correlates the received signal from the secondary synchronization channel (S-SCH) with all secondary synchronization codes (SSC), and identifies the maximum correlation value. The S-SCH is also only sent during the first 256 chips of every slot. One SSC is sent in every time slot. There are 16 different SSCs, and they can form 64 unique secondary SCH sequences. One sequence consists of 15 SSCs, and these sequences are arranged in such a way that in any nonzero cyclic shift less than 15 of any of the 64 sequences is not equivalent to some other sequence. This means that once the UE has identified 15 successive SSCs, it can determine the code group used as well as the frame boundaries (i.e., frame synchronization).

The use of CPICH (Common Pilot Channel)

CPICH stands for Common Pilot CHannel in UMTS and some other CDMA communications systems.
In WCDMA FDD cellular systems, CPICH is a downlink channel broadcast by Node Bs with constant power and of a known bit sequence. Its power is usually between 5% and 15% of the total Node B transmit power. A common the CPICH power is 10% of the typical total transmit power of 43 dBm.
The Primary Common Pilot Channel is used by the UEs to first complete identification of the Primary Scrambling Code used for scrambling Primary Common Control Physical Channel (P-CCPCH) transmissions from the Node B. Later CPICH channels provide allow phase and power estimations to be made, as well as aiding discovery of other radio paths. There is one primary CPICH (P-CPICH), which is transmitted using spreading code 0 with a spreading factor of 256, notationally written as Cch,256,0[1]. Optionally a Node B may broadcast one or more secondary common pilot channels (S-CPICH), which use arbitrarily chosen 256 codes, written as Cch,256,n where 0 < n < 256.
A UE searching for a WCDMA Node B will first use the primary and secondary synchronisation channels (P-SCH and S-SCH respectively) to determine the slot and frame timing of a candidate P-CCPCH, whether STTD is in use, as well as identifying which one of 64 code groups is being used by the cell. Crucially this allows to UE to reduce the set of possible Primary Scrambling Codes being used for P-CPICH to only 8 from 512 choices. At this point the correct PSC can be determined through the use of a matched filter, configured with the fixed channelisation code, looking for the known CPICH bit sequence, while trying each of the possible 8 PSCs in turn. The results of each run of the matched filter can be compared, the correct PSC being identified by the greatest correlation result.
Once the scrambling code for a CPICH is known, the channel can be used for measurements of signal quality, usually comprising of RSCP and Ec/I0. Timing and phase estimations can also be made, providing a reference that helps to improve reliability when decoding other channels from the same Node B.

Synchronisation Channel (SCH)

Synchronisation Channel (SCH)

The Synchronisation Channel (SCH) is a downlink signal used for cell search. The SCH consists of two sub channels, the Primary and Secondary SCH. The 10 ms radio frames of the Primary and Secondary SCH are divided into 15 slots, each of length 2560 chips. Figure illustrates the structure of the SCH radio frame

Figure: Structure of Synchronisation Channel (SCH)The Primary SCH consists of a modulated code of length 256 chips, the Primary Synchronisation Code (PSC) denoted c_p in figure, transmitted once every slot. The PSC is the same for every cell in the system.The Secondary SCH consists of repeatedly transmitting a length 15 sequence of modulated codes of length 256 chips, the Secondary Synchronisation Codes (SSC), transmitted in parallel with the Primary SCH. The SSC is denoted c_s^i,k in figure 18, where i = 0, 1, …, 63 is the number of the scrambling code group, and k = 0, 1, …, 14 is the slot number. Each SSC is chosen from a set of 16 different codes of length 256. This sequence on the Secondary SCH indicates which of the code groups the cell’s downlink scrambling code belongs to. The primary and secondary synchronization codes are modulated by the symbol a shown in figure 18, which indicates the presence/ absence of STTD encoding on the P-CCPCH and is given by the following table:

P-CCPCH STTD encoded	a = +1
P-CCPCH not STTD encoded	a = -1

RRC Connection Establishment Procedure

RRC Connection Establishment Procedure

RRC connection establishment is shown in the figure

The RRC layer in the UE leaves the idle mode and initiates an RRC connection establishment by sending a RRC Connection Request message using transparent mode  RLC on CCCH logical channel. This logical channel will be mapped onto RACH transport channel by MAC. The Physical channel maps this RACH onto PRACH and transmits this message to network. Remember that the UE cannot send such a request message spontaneously through PRACH, because this PRACH will be used by all the UEs in the cell. So the UE will listen to AICH channel to know the time slot assigned for this UE to use PRACH. (To know more about this click here).
BTS is completely transparent to this message, because it doesn’t have any RRC layer .
On the network side, upon the reception of RRC Connection Request, the RRC layer performs admission control, assigns an s-RNTI for the RRC connection and selects radio resource parameters (such as transport channel type, transport format sets etc). If a DCH is to be established, CPHY-RL-Setup and CPHY-TrCH-Config request primitives (transmitted as one RADIO LINK SETUP PDU) are sent to all Node Bs that would be involved in the channel establishment. The physical layer operation is started and confirmation primitives are returned from each Node B. RRC configures parameters on layer 2 to establish the DCCH logical channel locally. The selected parameters including the RNTI, are transmitted to the UE in an RRC Connection Setup message using unacknowledged mode on the CCCH logical channel.
Upon reception of the RRC Connection Setup message, the RRC layer in the UE configures the L1 and L2 using these parameters to locally establish the DCCH logical channel. In case of DCH, layer 1 indicates to RRC when it has reached synchronisation.
The RLC signalling link is locally established on both sides. The establishment can be mapped on either RACH / FACH or DCH by MAC. When the UE has established the RLC signalling link, it transmits an RRC Connection Setup Complete message to the network using acknowledged mode on the DCCH.

Example for a Data flow through MAC layer.

Example for a Data flow through MAC layer.

The logical channels coming from higher layer – RLC will be terminating in the MAC. It is the functionality of MAC to perform logical to transport channel mapping. Many number of logical channels can be mapped into one transport channel.
Here I consider the logical channels DCCH/DTCH that are coming from RLC. A data packet arriving from DCCH/DTCH logical channel triggers the Transport channel type selection. In this example, the FACH transport channel is selected.
Next, the multiplexing unit adds a C/T field – this indicatesthe logical channel instance where the data originates. For common transport channels, such as FACH, this field is always needed. For dedicated transport channels (DCH) it is needed only if several logical channel instances are configured to use the same transport channel. The C/Tfield is 4 bits, thereby allowing the mapping of upto 15 logical channels to a transport channel.(Value 1111 is reserved for future use).
The priority tag (not part of the MAC PDU) for FACH and DSCH is set in MAC-d and used by MAC-c/sh when scheduling data onto transport channels. Priority for FACH can be set per UE; for DSCH it can be set per PDU. A flow control function in Iur interface is needed to limit buffering between MAC-d and MAC-c/sh (which can be located in different RNCs). After receiving the data from MAC-d, the MAC-c/sh entity first adds the UE identification type (2 bits), the actual UE identification (C-RNTI 16 bits, or U-RNTI 32 bits), and the Target Channel Type Field (TCTF, in this example 2 bits) which is needed to separate the logical channel type using the transport channel .Now the MAC PDU is ready and the task for the scheduling/priority handling function is to decide the exact time when the PDU is passed to Layer 1 via the FACH transport channel (with an indication of the transport format to be used).

Definition of 3G

Definition: 3G is the third generation of mobile phone standards and technology. 3G supersedes 2 Gtechnology and precedes 4G technology. 2.5 was a temporary bridge between 2G and 3G.
3.5G stands for the HSDPA (High speed down link packet access), which provides very high downlink rate. The theoretical data rate for HSDPA in UA06 release in 14.4 Mbps.
3.75G stands for HSUPA(High speed Uplink packet access),which provides high data rates in uplink.
The first pre-commercial 3G network launched in May 2001 by NTT DoCoMo in Japan. The network was branded as FOMA. Following the first pre-commercial launch, NTT DoCoMo again made history with the first commercial launch of 3G in Japan on Oct. 1, 2001

Dual Cell HSDPA

Dual-Cell HSDPA (also known as: Dual-Carrier HSPA or Dual-Cell HSPA) is a wireless broadband standard based on HSPA that is defined in 3GPP UMTS release 8.
Dual Cell (DC-)HSDPA is the natural evolution of HSPA by means of carrier aggregation in the downlink[1]. UMTS licenses are often issued as 10 or 15 MHz paired spectrum allocations. The basic idea of the multicarrier feature is to achieve better resource utilization and spectrum efficiency by means of joint resource allocation and load balancing across the downlink carriers.
An advanced HSPA network can theoretically support up to 28Mbit/s and 42Mbit/s with a single 5 MHz carrier for Rel7 (MIMO with 16QAM) and Rel8 (64-QAM + MIMO), in good channel condition with low correlation between transmit antennas. An alternative method to double the data rates is to double the bandwidth, i.e. 10 MHz by using DC-HSPDA. Additionally, some diversity and joint scheduling gains can also be expected [2] with improved QoS for end users in poor environment conditions where existing techniques such as MIMO spatial multiplexing cannot be used to increase data rates. In 3GPP a study item was completed in June 2008. The outcome can be found in a technical report [3]. New HSDPA UE categories 21-24 have been introduced that support DC-HSDPA. DC-HSDPA can support up to 42Mbit/s, but unlike HSPA, it does not need to rely on MIMO transmission.
From Release 9 onwards it will be possible to use DC-HSDPA in combination with MIMO used on both carrier[4]. The support of MIMO in combination with DC-HSDPA will allow operators deploying Release 7 MIMO to benefit from the DC-HSDPA functionality as defined in Release 8. While in Release 8 DC-HSPDA can only operate on adjacent carriers, Release 9 allow that the paired cells can operate on two different frequency bands.