CS 6956 Wireless & Mobile Networks April 1st 2015

The  SIM  Card  

Certain  phones  contain  SIM  lock  and  thus  work  only  with  the  SIM  card  of  a  certain  operator.  However,  this  is  not  a  GSM  restriction  –  introduced  by  mobile  network  operators  to  ensure  that  a  subsidized  phone  is  used  only  with  SIM  cars  of  their  network.  

Contains  IMSI  (International  Mobile  Subscriber  ID)  and  secret  key  K  (for  authenticating  with  the  home  network)  

There  are  tools  to  read  parameters  of  the  SIM  card  except  sensitive  parameters  that  are  read  protect.  The  sensitive  parameters  are  accessed  with  a  special  unlock  code  that  is  not  available  to  the  end  user.  

Can  execute  programs  that  the  network  operator  installs  on  it  (through  the  SAT  –  SIM  applications  toolkit).  

Here  is  a  picture  of  the  SIM  card  components  from  Martin  Sauter’s  book.  

 

Universal Mobile Telecommunication System (UMTS)

• as much an evolution as a revolution Design consideration: Increase in processing power enables use of much more complex intensive air interface transmission methods that utilize the scarce bandwidth on the air interface more effectively (in comparison to GSM). 3GPP – responsible for evolving the GSM, UMTS, and LTE standards Release 99- first release of UMTS Completely redesigned Radio Access Network (RAN) UMTS terrestrial Radio Access Network (UTRAN) R99

• Up to 384 kbps • BSC (in 2G) called Radio Network Controller • BTS (in 2G) called NodeB • MS (in 2G) called User Equipment (UE) • Europe and Asia – 12 blocks of 5 MHz each for uplink and downlink (1920 – 1980 MHz; 2110 –

2170 MHz) • Different bands require additional circuitry in the UE. • Security Enhancements – authenticate the network, add integrity protection, better cipher

algorithms • Core network about the same as GPRS network • Used ATM in interface from RNC to NodeB (instead of frame relay) • Seamless voice handover from GSM to UMTS and vice versa • Data session handover is not that seamless due to lower rate of GSM/GPRS

UMTS uses CDMA Code Division Multiple Access (CDMA)

Most of the material here is from the Wireless Networks book (2nd edition) by William Stallings

- Multiplexing technique used with spread spectrum - Start with data signal with rate D (call it bit data rate) - Break each bit into k chops according to a fixed pattern that is specific to each user -> user’s code - New channel – chip data rate of kD chips per second - Figure below shows three codes for three different users

Receiver R receives pattern, d = < d1, d2, d3, d4, d5, d6 >, it performs the following decoding function.

Su(d) = d1 X c1 + d2 X c2 + … + d6Xc6 CA = < 1, -1, -1, 1, -1, 1>, let SA be decoded value at user A. when bit 1 is transmitted, d = < 1, -1, -1, 1, -1, 1 >, SA = 6 when bit 0 is transmitted, d = < -1, 1, 1, -1, 1, -1 >, SA = -6 If the value is not -6 or +6, either someone else (not user A) is sending information or the information is received in error. When user B sends a 1, d = < 1, 1, -1, -1, -1, 1 >, d received at A will result in SA = 0. Thus, unwanted signal from B does not show up at all. Let sA and sB be transmitted signals. Then, SA (sA + sB) = SA(sA) + SA(sB) = SA(sA), since the decoder ignores B when it is using A’s code.

User A

Code Message "1101" Encoded

User B

User C

Figure 7.10 CDMA Example

1 –1 –1 1 –1 1

1 1 –1 –1 1 1

1 1 –1 1 1 –1

The codes of A and B that have the property that SA(CB) = SB(CA) = 0 are called orthogonal. This is a desirable characteristic of the code but there are not that many orthogonal codes. The more common case is that SX(CY) is small in absolute value when X is not equal to Y. Now, when using the codes for users A, B, and C, SB(CC) = SC(CB) = 2. The signal from B (or C) makes a small contribution to the decoded signal at C (or B). Using the decoder Su, the receiver can sort out transmission from u even when there are other users broadcasting in the same channel. If these competing signals are send with higher power, then the system breaks down. Power control is very important in CDMA. In practice, the CDMA receiver can filter out the contribution from unwanted users or they appear as low-level noise. However, if there are many users competing for the channel with the user the receiver is trying to listen to, or if the signal power of one or more competing signals is too high, the system breaks down. UMTS Frequency and Cell Planning - All cells in UMTS radio network can use the same frequency - All neighboring cells use the same frequency - If a new cell is installed to increase the bandwidth in an area that is already covered by other cells,

the most important task in a UMTS network is to decrease the transmission power of the neighboring cell.

- Near-far effect: The network can instruct each handset (1500 times per second) to adapt its transmission power. The users that are close by are instructed to transmit at a low power. This power control increases the operating time of the mobile device battery.

- Actual transmission of a bit stream -> use QPSK, e.g., shown in one of the earlier classes.

Soft handover – CDMA allows a user to communicate with multiple base stations (Node-Bs) at the same time (not supported in GSM/ GPRS/LTE). The two figures below (from Martin Sauter’s book) show the soft handover from the network’s and from the device’s viewpoint.

UMTS also has logical channels – common and dedicated channels

Long term Evolution (LTE) [Primary from Sauter’s book]

CDMA (used in UMTS) does not scale very well, primarily due to inter-symbol interference.

Use OFDM

• That transmits data over narrowband carriers of 180 kHz each • Data stream split into many slower data streams that are transmitted simultaneously • Attainable data rate comparable to UMTS in the same bandwidth but the multipath effect is severely

reduced

If less than 5 MHz is available, LTE can easily adapt and the number of narrowband carriers is simply reduced

LTE – 1.25 MHz – 20 MHz (20 MHz can result in beyond 100 Mbps under very good signal conditions)

LTE must support MIMO resulting in even higher data rates