1. SAE architecture Interworking with 2G/3G Networks MME UPE SAE GW Operator IP services (including IMS, PSS,...) Non-3GPP IP Access Evolved Packet Core S11 S2 S3 S4 S7 S6 SGi S1 Gb Iu Rx+ LTE Uu X2 E-UTRAN PDN SAE GW S5 eNB cell eNB cell GERAN UTRAN HSS GPRS Core PCRF Um Uu LTE Uu

2.  LTE uses OFDM for the Downlink Link.  LTE uses SC-FDMA for the Uplink. LTE Air Interface UE eNB cell OFDMA D/L Tx SC- FDMA U/L Tx

3. OFDM Basic Concepts  OFDM is a multicarrier system.  Orthogonal Frequency Division Multiplex (OFDM) is a form of transmission that uses a large number of close spaced carriers that are modulated with low rate data.  Normally these signals would be expected to interfere with each other, but by making the signals orthogonal to each another there is no mutual interference.

4. Ch.1 Ch.2Ch.3Ch.4Ch.5Ch.6Ch.7Ch.8Ch.9Ch.10 Ch.3Ch.5Ch.7Ch.9 Ch.2Ch.4Ch.6Ch.8Ch.10 Ch.1 Conventional multicarrier techniques Orthogonal multicarrier techniques OFDM 50% bandwidth saving frequency A B Traditional FDM Signal and OFDM

5. The OFDMA refers indeed to the Orthogonal FDMA as the parameters for the sub-carrier are chosen to that neighboring sub-carriers have zero value the desired sampling point for any sub-carrier. Total transmission bandwidth Maintaining sub-carriers orthogonal Zero value for other sub-carriers. Sampling point for a single sub-carrier. 15 kHz

6. Multi ‐ Path Propagation and ISI

7.  The cancellation of inter ‐ symbol interference(ISI) makes hardware design of the receivers more complex.  In WCDMA for instance the RAKE receiver requires a huge amount of DSP capacity.  One of the goals of future radio systems is to simplify receiver design. Multi ‐ Path Propagation and ISI

8. Cyclic Extension (CE) Cyclic extension is the part of the symbol to be transmitted, it is copied from the end and is attached at the beginning of the symbol. OFDM symbol before CE addition CE OFDM symbol duration after CE addition CE is also known as Cyclic Prefix (CP) or Guard Period (GP) usable symbol

9. Narrowband Interference Rejection  Easy to Avoid/Reject Narrowband Dominant Interference.  Less Interfered Part of the Carrier Can Still Be Used. Interference Avoidance

10. FFT-based OFDM System Serial-to- Parallel Converter Signal Mapper IFFT Parallel- to-Serial Converter Guard Interval Insertion Serial Data Input x bits D/A & Low pass Filter Up- Converter Down- Converter A/D Guard Interval Removal Serial-to- Parallel Converter FFT One-tap Equalizer Signal Demapper Parallel- to-Serial Converter Serial Data Output x bits Channel Time Frequency Subchannels Fast Fourier Transform Guard Intervals Symbols

11. LTE Frame Structure 1 Frame of 10 ms duration, 20 slots 1 Sub frame of 1ms, 2 slots, 1 TTI 1 Slot of 0.5 ms, 7 or 8 OFDMA symbols

12. What is Resource Element (RE)? A Resource Element (RE) is one OFDM symbol (in the time domain) of 1 subcarriers (in the frequency domain). It is the minimum unit of data allocation and power control. However resource allocation is always done as a group of REs called Resource Block.

13. OFDMA time - frequency grid a subcarrier an OFDMA symbol time frequency One RE

14. What is Resource Block (RB)? A Resource Block (RB) is defined as set of 7 consecutive OFDM symbols in the time domain and set of 12 consecutive subcarriers in the frequency domain. The resource block in the specifications refers to 0.5 ms slot, but the resource allocation is done anyway with the 1 ms resolution in the time domain (per sub-frame or 1 TTI). It is the task of the scheduler to assign resource blocks to physical channels belonging to different users.

15. What is Resource Block (RB)? Time t Frequency f 1 symbol 15 KHz 7 symbols 12 carriers 180 KHz

16. OFDMA- time frequency multiplexing

17. LTE downlink frequency profile Channel BW1.435101520 Transmission BW1.082.74.5913.518 No. of RBs615255075100 FFT size128256512102415362048

18. Single-carrier FDMA LTE uses OFDMA for downlink but not for uplink. Instead of OFDMA,LTE uses SC-FDMA in uplink. Why ?

19. Why SC FDMA in Uplink ?  The OFDM transmission consists of several parallel sub- carriers in frequency domain. In the time domain this corresponds to multiple sinusoidal waves with different frequency components and occupying the system bandwidth with steps of 15KHz.  The combined signal envelope vary strongly.  This causes challenges to the amplifier design.

20. … …  The transmitted OFDM signal should be seen as a sum of sinusoid.  This is not suited for a highly linear, power efficient terminal amplifier.  The envelope needs to be with as low Peak-to-Average Ratio (PAR) as possible. Power Amplifier,problem for you IFFT Frequency domain QAM modulated inputs Time domain signal (sum of sinusoids) FFT Frequency domain QAM modulated outputs Why SC FDMA in Uplink ?

21. Time domain signal (sum of sinusoids) sinusoidal wave max. avg. max. avg. Back off i/p o/p For high PA efficiency back off must be minimum. High back off need high power consumption

22. Why SC FDMA in Uplink ?  Power consumption in user equipment (UE) terminals is limited by battery.  OFDM requires large dynamic range due to high peak to average power ratio(PAPR).  Liner power amplifiers with wide dynamic range have bad efficiency.

23. SC-FDMA DFT spread OFDM (DFTS-OFDM) is a transmission scheme that can combine the desired properties for uplink transmission i.e. :- Small variation in the instantaneous power of the transmitted signal (single carrier property). Possibility for low complexity high quality equalization in the frequency domain. Possibility for FDMA with flexible bandwidth assignment. SC-FDMA can be referred as DFTS- OFDMA

24. Basic principle of DFTS-OFDMA S- to- P converter Size-M DFT Size-N IDFT M 0 0 0 Serial Bit stream P to s Serial Bit stream N > M Unused inputs of IDFT is set to zero

25. S C constellation mappi ng S-to-P converter Sub carrier mapping N- point IDFT M- point DFT P-to-S converter CP insertion RFRF S C detector and constellation demappi ng P-to-S converter Frequency domain equalizer N- point DFT M- point IDFT S-to-P converter CP removal RFRF SC FDMA Functional blocks SC-FDMA Transmitter SC-FDMA receiver Bit stream M < N

26. How does a SC FDMA signal look like SC-OFDMA signal is similar to OFDMA signal, but…  In OFDMA, each sub-carrier only carries information related to one specific symbol.  In SC-OFDMA, each sub-carrier contains information of all transmitted symbols.

27. OFDMA vs SC FDMA OFDMA Data symbol occupy 15 kHz for one OFDM symbol period SC-FDMA Data symbol occupy N x15 kHz for 1 / N SC-FDMA symbol period

28. frequency User multiplexing in frequency domain Smallest uplink bandwidth 180 kHz. Largest 20 MHz (terminal are required to able to receive & transmit up to 20 MHz, depending on the frequency band though.) Terminal 1 Transmitter IFFT FFT Terminal 2 Transmitter FFT IFFT frequency BTS Receiver frequency Uplink Multiple Access – SC-FDMA