Florida Institute of technologies ECE 5221 Personal Communication Systems Prepared by: Dr. Ivica Kostanic Lecture 12: Frequency allocation and channelization Spring 2011

Florida Institute of technologies Page 2  Duplexing  Spectrum allocation in the US  Frequency division multiple access (FDMA)  Time division multiple access (TDMA)  Examples Outline Important note: Slides present summary of the results. Detailed derivations are given in notes.

Florida Institute of technologies Duplexing schemes in cellular networks  Cellular communications is full duplex oCommunication from MS to BS -> uplink oCommunications from BS to MS -> downlink  Two ways for full duplex oFrequency Division Duplexing (FDD) oTime Division Duplexing (TDD) Page 3  Frequency Division Duplexing (FDD) o More common o Uses paired spectrum allocation o One part (usually lower in frequency) – uplink o Second pert (usually higher in frequency) – downlink o Lower frequencies used for UL due to slightly better propagation Note: frequency separation between UL and DL is referred to as the duplexing separation / duplexing space

Florida Institute of technologies Case study 1. US cellular frequency band  Spectrum is around 850 MHz  Two licenses A and B (25MHz each)  Initial licenses awarded in 1983 oA – newcomer oB – existing landline carrier  Additional spectrum allocated in 1989  License A oDownlink:  MHz (A’’)  MHz (A)  (A’) oUplink:  MHz (A’’)  MHz (A)  MHz (A’)  License B oDownlink:  MHz (B)  MHz (B’) oUplink  MHz (B)  MHz (B’) Page 4 Spectral plan for US cellular band

Florida Institute of technologies Case study 2: US PCS frequency band  Six licenses (A-F)  Large licenses (2 times 15 MHz): A,B,C  Small licenses (2 times 5MHz) D, E, F  Auctioned in 1995  Duplexing space 80MHz LicenseDL [MHz]UL [MHz]Amount of spectrum [MHz] A x 15 D x 5 B x 15 E x 5 C x 15 F x 5 Page 5 Note: Original rules prevented operators from owning spectrum in both 850 and 1900MHz. This has changed in PCS spectrum allocation

Florida Institute of technologies Time division duplexing  Uses same spectrum for UL and DL  Spectrum access is divided in time between UL and DL  Allocation of time slots may be managed in a dynamic manner – accommodates shift in traffic patterns Page 6 Time Division Duplexing (TDD) Original spectrum allocation for 3G. Note both paired and unpaired spectrum bands World wide spectrum allocations:

Florida Institute of technologies Frequency Division Multiple Access (FDMA)  Allocated spectrum separated in smaller frequency bands  A pair of segments is referred to as the channel (one frequency for UL and one for DL)  Number of available channels depend on the total amount of spectrum and channel bandwidth of the cellular technology  Users that are geographically close operate on different channels Page 7 Spectrum channelization Note: The mobiles are co time, but do not interfere due to frequency separation

Florida Institute of technologies FDMA Example Consider deployment of GSM in A block of PCS band. Calculate the number of channels that can be accommodated. GSM channel is 200KHz wide. Page 8 Number of channels Guard band – prevents interference with adjacent bands

Florida Institute of technologies GSM – Frequency ARFCN calculations Page 9 ARFCN – Absolute Radio Frequency Channel Number Example – US PCS allocation 22

Florida Institute of technologies Time Division Multiple Access (TDMA)  Multiple users share the same frequency channel  The sharing is done in time domain  Only one user access the channel in a given time  Portions of time allocated to the user are called time slots  The number of users sharing the channel is technology dependent (3-16) Page 10 Note that: Rc = N x Ru

Florida Institute of technologies Example. TDMA in GSM  Channel is shared between eight users  User does not transmit and receive at the same time  Transmission occurs in “accumulate and burst” fashion oHas to be digital oChanel bandwidth larger than the single user rate Page 11 Note: for good portion of time phone does not transmit or receive

Florida Institute of technologies Near-far problem in TDMA systems  In TDMA synchronization between users – vital  Delay of the burst for the further mobiles is larger  Due to different delays – burst may collide  Te remedy the problem, mobiles advance their transmission  The amount of time advancement is determined by base station and communicated to the mobiles Page 12