1. 4G Mobile Communications

2. History
In March 2008, the International Telecommunications Union-Radio (ITU-R) specified a set of requirements for 4G standards, named the International Mobile Telecommunications Advanced (IMT-Advanced) specification, setting peak speed requirements for 4G service at 300 Mbit/s for high mobility communication (such as from trains and cars) and 1Gbit/s for low mobility communication (such as pedestrians and stationary users).
Since the first-release versions of Mobile WiMAX (first used in South Korea in 2007) and LTE (in Oslo, Norway and Stockholm, Sweden since 2009 ) support much less than 1 Gbit/s peak bit rate, they are not fully IMT-Advanced compliant, but are often branded 4G by service providers.
On December 6, 2010, ITU-R recognized that these two technologies, as well as other beyond-3G technologies that do not fulfill the IMT-Advanced requirements, could nevertheless be considered "4G", provided they represent forerunners to IMT-Advanced compliant versions .

3. During the spring 2011 above two system provide their advanced version as: Mobile WiMAX Release 2 (also known as WirelessMAN-Advanced or IEEE m) and LTE Advanced (LTE-A, Based on UMTS 3G technology) and promising speeds in the order of 1 Gbit/s in 2013.

4. Comparison of 3G and 4G 3G 4G
Data Rates of 100 Kbps to 2 Mbps Goal is 'to provide multimedia multirate mobile communications anytime and anywhere'. Connection between the cellular world and the wired Internet firmly established.
Mobile devices used mainly for Human-to-Human and Human-to-Machine communication
Data Rates up to 100 Mbps
Expansion on the 3G goal to provide a wider range of new and improved multimedia services.
Integration of broadcast, cellular, cordless, Wireless LAN, short-range and fixed wire systems to appear as a single seamless network.
Not only the 3G modes of communication but also characterized by a great deal of Machine-to-Machine traffic

5. Some Key Challenges Coverage
Transmit power limitations and higher frequencies limit the achievable cell size
Capacity
Current air interfaces have limited peak data rate, capacity, and packet data capability
Spectrum
Lower carrier frequencies (< 5 GHz) are best for wide-area coverage and mobility 5

6. WiMAX
Wi-MAX : The Worldwide Interoperability for Microwave Access, is a technology aimed at providing wireless data over long distances It is based on the IEEE standard.
Fig.1

7. WiMAX
In 1998 IEEE protocol was developed to provide high speed service of WMAN (Wireless Metropolitan Area Network). Next two new version of above protocol were found as: IEEE d (in 2004) was developed to support high speed wireless data service of fixed user and its later version IEEE e (in 2005) supports both fixed and mobile users.
With the advent of OFDMA based IEEE e, research is now going on to implement VoIP service with adaptive modulation and channel coding (MCS) scheme. To enhance the throughput of the wireless system the modulation and coding scheme of the transmitter is changed according to the fading condition of the channel.
Therefore the service becomes a variable bit rate service where the bit rate depends on the fading condition of the wireless channel.

8. Three common types of BW allocation algorithms are: Dedicated Resource Allocation (Unsolicited Grand Service known as UGS Algorithm) where fixed amount of BW is allocated to each user hence possibility of waste of BW when a user needs to data send data at low rate; Polling-Based Resource Allocation (Real-Time Polling Service called rtPS Algorithm) where BS allocates the BW dynamically therefore incurs some protocol overhead and delay; Hybrid Resource Allocation Algorithm is the combination of above two.
WiMAX also can be used as a complementary system to Wi-Fi. Both of the two major 3G systems: CDMA2000 and UMTS, compete with WiMAX.

9. WiBro, Korean version of WiMAX has been deployed in Korea.
WiFi and WiMAX are the B3G (Beyond 3G) systems. WiMAX may be an interim system of a 4G system.

10. Some important features of WiMAX are given below:
OFDM in physical layer: The access technique used in physical layer of WiMAX is OFDM; where the high speed serial data is converted to low rate parallel streams and each stream is modulated by separate carrier each one is known as subcarrier. Subcarriers are mutually orthogonal and deals with low data rate hence can protect multipath fading.
Very high peak data rates: The data rate of WMAX is 70Mbps under the channel of bandwidth of 20 MHz. The rate can be further increased using space division multiplexing i.e. incorporation of multiple antennas.

11. Adaptive Modulation and Coding: The IEEE 802
Adaptive Modulation and Coding: The IEEE e standard changes modulation and channel coding scheme based on received SNR. For example a SS close to the BS can use a high modulation scheme (more bits per symbol) i.e. the system can get more capacity but when the SS is at the cell boarder the system permits lower modulation scheme (increased signal space on orthogonal basis function coordinate system) to avoid huge symbol error rate. Therefore the system can overcome the time selective fading (the channel condition is better at some instant than other).
Error Correction Techniques: WiMAX incorporates two types of strong error correction techniques: FEC (Forward Error Correction) for multimedia traffic and ARQ (Automatic Repeat Request) for data traffic to improve throughput. 

12. Support for TDD and FDD: Like mobile cellular communication it supports both FDD (Frequency division duplexing) and TDD (Time division duplexing), as well as a half-duplex FDD. Above features provide the flexibility of using same or different carriers for up and down link.
Time Division Duplexing
Time division duplexing (TDD) refers to the interleaving of transmission and reception of data on the same frequency. A common frequency is shared between the upstream and downstream, the direction in transmission being switched in time.
Frequency Division Duplexing
Frequency division duplexing (FDD) refers to the simultaneous transmission and reception of data over separate frequencies, allowing for bidirectional full-duplex communications.

13. Fig.2 IEEE 802.16 general architecture

14. OFDMA Based WiMAX Network
We consider a single cell in a WiMAX network with a base station and multiple subscriber stations (Fig.3). Each subscriber station serves multiple connections. Admission control is used at each subscriber station to limit the number of ongoing connections through that subscriber station. At each subscriber station, traffic from all users for uplink connections are aggregated into a single queue.

15. Fig.3 System model
The size of this queue is finite (i.e., X packets) in which some packets will be dropped if the queue is full upon their arrivals. The OFDMA transmitter at the subscriber station receives packets and transmits them to the base station. The base station may allocate different number of subchannels to different subscriber stations. For example, a subscriber station with higher priority could be allocated more number of subchannels.

16. IEEE 802 Activities Wired Wireless 802.3: Ethernet
802.17: Packet Ring (new)
Wireless
802.11: Wireless LAN
Local Area Network
802.15: Wireless PAN
Personal Area Network (e.g. BluetoothTM)
802.16: WirelessMANTM
Metropolitan Area Networks

18. Wireless Technology Evolution to 3.9G
1. What is 4G?
Wireless Technology Evolution to 3.9G
CDMA
IEEE Cellular
IEEE LAN
GSM/UMTS
CDMA
(IS-95A)
GSM
TDMA
IS-136
IEEE
802.16
IEEE
802.11 2G
CDMA
(IS-95B)
GPRS
802.11g
2.5G
cdma
2000
E-GPRS
EDGE
WCDMA
FDD/TDD
TD-SCDMA
LCR-TDD
802.11a 3G
3.5G
1xEV-DO
Rev 0/A/B
HSDPA
FDD/TDD
HSUPA
FDD/TDD
Fixed WiMAX
802.16d
WiBRO
802.11g
UMB
802.20
LTE
E-UTRA
HSPA+
Mobile WiMAX
802.16e
802.11n
3.9G
Fig.4

19. In a hierarchical telecommunications network the backhaul portion of the network comprises the intermediate links between the core network or backbone, of the network and the small sub-networks at the "edge" of the entire hierarchical network.

22. Wi-Fi
Wi-Fi, which stands for “wireless fidelity,” is a radio technology that networks computers so they connect to each other and to the Internet without wires. Users can share documents and projects, as well as an Internet connection, among various computer stations and easily connect to a broadband Internet connection while traveling. By using a Wi-Fi network, individuals can network desktop computers, laptops, and PDAs and share networked peripherals such as servers and printers.

23. A Wi-Fi network operates just like a wired network, but without the restrictions imposed by wires. It uses radio technologies called IEEE a, b, or g to provide secure, reliable, fast wireless connectivity. A Wi-Fi network can be used to connect computers to each other, to the Internet, and to wired networks (which use IEEE or Ethernet). Wi-Fi networks operate in the unlicensed 2.4-and 5-GHz radio bands with an 11-Mbps (802.11b) or 54-Mbps (802.11a) data rate, or with products that contain both bands (dual band).

25. Layers of WiMAX Upper layers Service specific convergence layer
MAC sub-layer
Security sub-layer
Transmission convergence sub-layer
QPSK
16-QAM
64-QAM
Data link layer
Physical layer
Security Sublayer provides authentication, secure key exchange and encryption between SS and BS.
Fig.5 The protocol stack

26. PHY
Burst Uplink (A data burst (PDU) in a downlink or in an uplink consists of several slots).
Downlink
Mode A: continuous transmission stream supporting concatenation of Reed Solomon coding, interleaving, and convolutional coding for use in an FDD only system
Mode B: burst format supporting FDD with adaptive modulation as well as TDD and half-duplex FDD
Modulation
QPSK, 16-QAM, 64-QAM
Fig.6

27. Adaptive Modulation and Coding
An SS (subscriber Station) close to the BS could use a high modulation scheme, thereby giving the system more capacity. In contrast, a weak signal from a more remote subscriber might only permit the use of a lower modulation scheme to maintain the connection quality and link stability.
This feature enables the system to overcome time-selective fading.
The coding rate also change according received SNR of fading channel.

28. Modulation Coding Schemes (MCSs)
PDU → Packet Data Unit
SDU → Service Data Unit
lm → the number of TDMA slots /PDU

29. Uplink scheduling is feasible if the allocated uplink resources are less than the total of available resources (number of PDU/slot) Nslot,u.
Hence, we have
where the parameter lm is the size of the VoIP PDU, which is modulated with the mth MCS level after encoding and xm is the number of PDU at mth MCS level.

30. For example, we consider Nslot,u = 50 and M = 4
For example, we consider Nslot,u = 50 and M = 4. Then, the MCS-level distributions of packets are denoted as,
X =(x1, x2, x3, x4).
If the MCS-level distributions of six packets in the uplink queue are (0, 0, 0, 6) or (0, 0, 1, 5) and the MCS level of the seventh packet in the queue is not four, the BS schedules six packets according to the uplink feasibility condition.
X = (0, 0, 0, 6)
= *6 = 36 <50
X = (0, 0, 1, 5)
= *12 + 5*6 = 42 < 50

31. However, if the MCS level of the seventh packet is four, the BS can schedule more packets than six because the MCS-level distribution of seven packets becomes (0, 0, 0, 7) or (0, 0, 1, 6), which satisfies feasibility condition.
X = (0, 0, 0, 7)
= *7= 42 <50
X = (0, 0, 1, 6)
= *12 + 6*6= 48 <50

32. Service specific convergence layer
Transmission convergence sub-layer (TCS) converts MAC PDUs of variable size into proper-length (fixed size) FEC (Forward Error Correction) blocks.
Upper layers
Service specific convergence layer
MAC sub-layer
Security sub-layer
Transmission convergence sub-layer
QPSK
16-QAM
64-QAM

33. Data link layer
From the reference model as illustrated in Figure 7, there are three sub-layers in the data link layer composed of i) a security sublayer, ii) a MAC common part sublayer, and iii) a convergence sublayer. It provides only connection oriented service
Upper layers
Service specific convergence layer
MAC sub-layer
Security sub-layer
Transmission convergence sub-layer
QPSK
16-QAM
64-QAM
Fig.7 The protocol stack

34. Service Specific Convergence Sub-layer (CS):
The CS, which is the interface between the MAC layer and layer 3 of the network, receives data packets from the higher layer. These higher layer packets are known as service data unit (SDU).
The CS is responsible for performing all operations that are dependent on the nature of higher-layer protocol (ATM, IPv4, IPv6 etc), such a header compression and address mapping. The CS can be viewed as an adaptation layer that masks the higher-layer protocol.

35. Packet header suppression (PHS): At the transmitter it involves removing the repetitive part of the header of each SDU. For example, if the SDUs delivered to the CS are IP packets, the source and destination addresses contained in the header of each IP packet do not change from one packet to the next and thus can be removed before being transmitted over the air. Similarly at the receiver: the repetitive part of the header can be reinserted into the SDU before being delivered to the higher layer.
CS is also responsible for the mapping the higher layer address, such as IP address, of the SDUs into the identity of the PHY and MAC connections to be used for its transmission. The WiMAX MAC layer is connection oriented and identifies a logical connection between the BS and the MS by a unidirectional connection identifier (CID). The CID for UP and DL connections are different.

36. MAC Common Part Sublayer
The MAC layer takes packets from the upper layer (CS) and these packets are called MAC service data units (MSDUs) and organize them into MAC protocol data units (MPDUs) for transmission over the air.
The WiMAX MAC uses a variable length MPDU and offer a lot of flexibility to allow for their efficient transmission. For example multiple MPDUs of same or different lengths may be arranged into a single burst when they are destined to the same receiver.

37. Similarly , multiple MSDUs from the same higher-layer service may be concatenated into a single MPDU to save MAC header overhead.
Large MSDUs may be fragmented into smaller MPDUs and send across multiple frames. When an SDU is fragmented, the position of each fragment within the SDU is tagged by a sequence number. The sequence number enables the MAC layer at the receiver to assemble the SDU from its fragments in the correct order.
WiMAX has two types of PDUs, each with a very different header structure.
The generic MAC PDU is used for carrying data and MAC-layer signaling messages.
The bandwidth request PDU is used by the MS to indicate to the BS that more BW is required in UL, due to pending data transmission. A bandwidth request PDU consists only of a bandwidth-request header, with no payload or CRC.

38. Each MAC frame is prefixed is prefixed with GMH (generic MAC header).
Field (in SH) to indicate whether the payload is encrypted or not. If the payload is encrypted then the encryption key is also given.
Header CRC field is a checksum over the header only using the generator polynomial x8+x2+x+1. The length of this field is 8bits.
Packed fixed size MSDU
GMH
Other SH
CRC
…….
Fig.6 MAC PDU frame carrying several-fixed length MSDUs packed together
GMH → Generic MAC Header (used for carrying data and MAC-layer signaling messages)
SH → Sub-header

39. Generic MAC Header Fields
LEN
msb
(3) H T
CID msb (8)
LEN lsb (8) E C
Type (6 bits) rs v I
EKS
(2)
HCS (8)
CID lsb (8)
Generic MAC Header Fields
Field
Length
description HT 1
Header type (set 0 for such header) EC
Encryption control (0 = payload not encrypted; 1 = payload encrypted
Type 6
type
ESF
(1 = ES present; 0 = ES not present) CI
CRC indicator (1=CRC included; 0=CRC not included)
EKS 2
Encryption key sequence (index of the traffic encryption key and the initialization vector used to encrypt the payload)
Rsv
Reserved
LEN 11
Length of MAC PDU in bytes, including the header)
CID 16
Connection identifier on which the payload is to be sent
HCS 8
Header check sequence; generation polynomial x8+x2+x+1

40. Bandwidth Request MAC Header Fields
BW Req.
msb (11) H T
CID msb (8)
BWS Req. lsb (8) E C
Type (3 bits)
HCS (8)
CID lsb (8)
Bandwidth Request MAC Header Fields
Field
Length
Description HT 1
Header type (set 1 for such header) EC
Encryption control (set 0 for such header)
Type 3
type BR 19
BW request ( the number of bytes of UL BW requested by the SS for the given CID)
LEN 11
Length of MAC PDU in bytes, including the header
CID 16
Connection identifier
HCS 8
Header check sequence

41. FSH → Fragmentation Sub-header PSH → Packing Sub-header
GMH
Other SH
CRC
FSH
MSDU Fragment
Fig.8 MAC PDU frame carrying a single fragmented MSDU
GMH
Other SH
CRC
PSH
Variable size MSDU or
Fragment …
Fig.9 MAC PDU frame carrying several variable length MSDUs packed together
FSH → Fragmentation Sub-header
PSH → Packing Sub-header
The type of payload is identified by the sub-header immediately precedes it. For example FSH or PSH of above figure.

42. Generic MAC Header Format (Header Type (HT) = 0) BW Req. Header Format
msb
lsb
Generic MAC
CRC
MAC PDU
Header
payload (optional)
(optional)
(6 bytes)
LEN
msb
(3) H T
CID msb (8)
LEN lsb (8)
Generic MAC Header Format
(Header Type (HT) = 0) E C
Type (6 bits) rs v I
EKS
(2)
HCS (8)
CID lsb (8)
BW Req. Header Format
(Header Type (HT) =1)
BW Req.
msb (8) H T
CID msb (8)
BWS Req. lsb (8) E C
Type (6 bits)
HCS (8)
CID lsb (8)

43. Privacy (or Security) Sub-layer:
supporting authentication, secure key exchange, and encryption.

44. Evolution of LTE 1G 2G 3G 4G
2.5G

45. Comparison of LTE Speed

46. The LTE- Advanced (Long Term Evolution- Advanced) is 4G wireless service proposed by 3GPP (Third generation Partnership Project). In G LTE started its commercial service in Scandinavia. Two important features of LTE are: femtocell deployment and OFDMA-based physical layer access.
The architecture of LTE consists of two major parts: the E-UTRAN (Evolved Universal Terrestrial Radio Access Network) and the EPC (Evolved Packet Core). The first part provides air interface between MS or UE to BS and the second part is interconnected switching network called backbone or core network.

47. The EPC consists of six nodes:
Home Subscriber Server (HSS) is like the combination of HLR and AUC of UMTS or GSM 
The Packet Data Network (PDN) Gateway (P-GW) provides connectivity between UE and external packer switching network. It works like a gateway SGSN of UMTS.
The serving gateway (S-GW) works as a router whose function is to forward data between the BS and the PDN gateway. It also works as the mobility anchor of eNB handovers and do the similar job between LTE and other 3GPP technologies. 

48. The MME (for Mobility Management Entity) deals with the signaling (between UE and CR) related to mobility of users, paging of UE in idle-mode and security for E-UTRAN access.
The Policy Control and Charging Rules Function (PCRF): This module works like: Packet filtering and billing on flow basis. 
ePDG (Evolved Packet Data Gateway) provides secured data transmission between UE to EPC over an untrusted non-3GPP access.

49. Fig.10 Architecture of LTE
S-GW
HSS
P-GW
E-UTRAN
Macro
Femto
Trusted non 3GPP access
ePDG
Untrusted non 3GPP access
Fig.10 Architecture of LTE