By Don Hanley, Senior Consultant - 2/2009

1xEV-DO and LTE networks are surprisingly similar in many respects, but the terms, labels and acronyms they use are very different. How can a 1xEV-DO operator make sense of this new jargon?

Introduction

As 4G technologies like Mobile WiMAX and Long Term Evolution (LTE) move closer to commercial reality, operators are beginning to understand the differences and the similarities between what they have currently deployed and what is coming down the road. Service providers who are contemplating the transition from 1xEV-DO to LTE will have to contend not only with new radio technologies and new network architectures, but with a whole new set of terms and concepts as well.

Both 1xEV-DO and LTE are designed to offer high-speed packet data services to mobile subscribers, so it should not be surprising that they have taken similar approaches to solving some of the challenges they both face. An engineer familiar with 1xEV-DO can get a head start with understanding LTE simply by learning the meaning of key LTE terms and associating them with their 1xEV-DO counterparts.

The following sections take various LTE concepts, grouped into related categories, and provide a brief explanation of each, along with the corresponding 1xEV-DO equivalent. In some cases, there is a one-to-one match between LTE and 1xEV-DO; in others, there simply is no equivalent concept. In most cases, however, there is generally something within 1xEV-DO that does the same thing as its LTE counterpart, under a different name or in a different location. We will identify the similarities and differences of LTE-EPC and 1x/1xEV-DO networks in various categories, including Air Interface, Access and Core Networks, Identities and Operations.

General

LTE is an evolution of the UMTS system defined by the 3G Partnership Project (3GPP), which is an offshoot of the European Telecommunications Standards Institute (ETSI). 1xEV-DO, on the other hand, is designed by the 3G Partnership Project 2 (3GPP2), which is associated with the North American Telecommunications Industry Association (TIA). Both 3GPP and 3GPP2 have mandates to develop specifications for wireless networks, but they have adopted rather different design philosophies, which are reflected in the resulting standards:

  • a) Flexibility versus optimization: In general, 3GPP prefers to create standards which are very open and flexible, allowing them to incorporate a variety of options, and to easily extend the interfaces to accommodate new features and capabilities. In contrast, 3GPP2 tends to define very optimized interfaces, which perform specific tasks as efficiently as possible. 1xEV-DO, for example, takes far fewer (and much shorter) messages to set up a data session than UMTS requires, but new features tend to require new sets of messages.
  • b) Authentication and security: 3GPP takes privacy very seriously, and very little information is sent over the air in its original form; encryption, temporary identifiers, message integrity checking, and user verification are basic elements of LTE signaling. 3GPP2 also includes security functions in the definition of 1xEV-DO, but they are optional extensions to the basic operation of the system.
  • c) User information: 3GPP makes extensive use of the Subscriber Identity Module (SIM), which stores user subscription data and related information separately from the phone itself. This allows a user to make use of a different device without losing their features and contacts. In 3GPP2 systems, the subscriber's identity and the phone's identity are usually tightly linked.

Despite the different mindsets behind the specifications, however, both 1xEV-DO and LTE do what they were designed to do quite well: deliver high-speed packet data to mobile users.

Air Interface

Not surprisingly, the greatest differences between LTE and 1xEV-DO lie in the air interface. 1xEV-DO is a CDMA-based system, using fixed 1.25 MHz channels, while LTE is a scalable OFDMA system, capable of using anywhere between 1.4 MHz and 20 MHz, divided into 15 kHz subcarriers. 1xEV-DO devices are assigned timeslots for downlink traffic, but can transmit at any time on the uplink (the hallmark of a CDMA system); LTE terminals must be explicitly allocated uplink and downlink non-overlapping resources to send and receive traffic. The Physical Layer descriptions of these two technologies are as different as night and day.

Nonetheless, they must both be capable of supporting multiple users simultaneously, of allowing new users to access the network, of tracking the terminal's location and redirecting traffic as the user moves. Key LTE terms relating to the air interface, and their 1xEV-DO equivalents, are listed here.

LTE Term

Meaning and Usage

1xEV-DO Equivalent

OFDMA

Orthogonal Frequency Division Multiple Access, physical layer of LTE Downlink

CDMA

SC-FDMA

Single Carrier Frequency Division Multiple Access, physical layer of LTE Uplink

CDMA

Subcarrier

A single 15 kHz radio channel

Radio channel

Symbol

A single 66.67 µs time period

Chip (0.81 µs)

Resource Element

The smallest unit of radio resources, one subcarrier for one symbol

n/a

Resource Block

The smallest block of resources that can be allocated, 12 subcarriers for 7 symbols (84 resource elements)[1]

n/a

Timeslot

7 consecutive symbols1

Slot

Subframe

2 consecutive timeslots

n/a

Frame

10 consecutive subframes, the basic transmission interval

Frame

Synchronization Signal

Periodic signal for synchronizing with and identifying cells

Sync message

Reference Signal

Periodic signal for transmission quality measurements

Pilot Channel

PBCH

Physical Broadcast Channel

Control Channel

PDSCH

Physical Downlink Shared Channel

Forward Traffic Channel

PDCCH

Physical Downlink Control Channel

Preambles + MAC channels

PCFICH

Physical Control Format Indicator Channel

DO Session

PHICH

Physical Hybrid ARQ Indication Channel

ARQ Channel

PRACH

Physical Random Access Channel

Access Channel

PUSCH

Physical Uplink Shared Channel

Reverse Traffic Channel

PUCCH

Physical Uplink Control Channel

MAC Channels

 

Access Network

Figure 1 illustrates an LTE eUTRAN, the radio access network. The eUTRAN has a flat architecture, with no centralized controller; instead each eNode B manages its own radio resources, and collaborates with other eNode B's over the X2 interface. The eNode B's connect to the core network over the S1 interface, to allow users to register with the network and send and receive traffic.

Key LTE terms relating to the access network, and their 1xEV-DO equivalents, are listed here:

LTE Term

Meaning and Usage

1xEV-DO Equivalent

eUTRAN

Evolved Universal Terrestrial Radio Access Network

AN

eNode B

Evolved Node B

Base station + RNC

Physical Layer Cell ID

Unique cell identifier

Pilot PN offset

UE

User Equipment

AT

X2

eNode B <-> eNode B interface

A13/A16/A17/A18

S1

eNode B <-> core network interface

A10/A11/A12

Uu

LTE air interface

Specified per 3GPP2 C.S0024 (IS-856)

Attach

A configured signaling path between the UE and the eNode B

DO Session

Radio Bearer

A configured and assigned radio resource

DO Connection

 

Core Network

The LTE and 1xEV-DO core networks are more similar than they are different; Figure 2 shows a view of the LTE Evolved Packet Core (EPC). Both are based on IP protocols, and support seamless access to packet-based services; both make use of Mobile IP to redirect traffic as the user moves through the network.

Key LTE terms associated with the core network, and their 1xEV-DO equivalents, are listed here:

LTE Term

Meaning and Usage

1xEV-DO Equivalent

EPC

Evolved Packet Core

Packet Data Network

MME

Mobility Management Entity

RNC + PDSN + AN-AAA

S-GW

Serving Gateway

PDSN + PCF

PDN-GW

Packet Data Network Gateway

HA

HSS

Home Subscriber System

AAA

PCRF

Policy Charging Rule Function

PCRF

MIP

Mobile IP

MIP

S1 Bearer

A configured traffic path between the eNode B and the S-GW

A10 + R-P Session

S5/S8 Bearer

A configured traffic path between the S-GW and the PDN-GW

MIP

EPS Bearer Service

A configured end-to-end traffic path between the UE and the PDN-GW (Radio Bearer + S1 Bearer + S5/S8 Bearer)

PPP + MIP

 

Operational Terms and Identifiers

When a mobile device arrives in the network, it must be recognized, configured and assigned resources, and its services must be maintained as it moves from cell to cell. Various terms associated with LTE operational functions, and their 1xEV-DO equivalents, are listed here:

LTE Term

Meaning and Usage

1xEV-DO Equivalent

UE

User Equipment (the mobile device)

Access Terminal (AT)

IMSI

International Mobile Subscriber Identity

IMSI [Mobile Country Code (MCC), Mobile Network Code (MNC) and  Mobile Identification Number (MIN) or

Mobile Directory Number (MDN)]

IMEI

International Mobile Equipment Identity

Mobile Serial Number (MSN) or Mobile Equipment Identity (MEID)

Downlink (DL)

Transmissions from the network to the mobile

Forward Link (FL)

Uplink (UL)

Transmissions from the mobile to the network

Reverse Link (RL)

Ciphering

Over-the-air privacy

Encryption

Attach

Initial registration process

UATI Assignment + DO Session Establishment + MIP Registration

MIB, SIB

Master Information Block and System Information Block

Quick Config + Sector Parameters + Access Parameters + DO Session

DCI, UCI

Downlink Control Information and Uplink Control Information

Traffic Channel Assignment

C-RNTI

Cell Radio Network Temporary Identifier

MAC Index

CQI

Channel Quality Indicator

DRC value

HARQ

Hybrid ARQ

HARQ

Handover

Redirection of traffic from one base station to another

Handoff

Measurement Control events A1, A2, A3, A4, A5, B1, B2

Thresholds for cell selection and handover

Pilot Add, Pilot Drop, Dynamic (Soft Slope) Thresholds

Conclusion

A simple description in a table does not convey the full complexity of a concept; a detailed understanding of LTE's technologies, architectures and interfaces is needed to fully appreciate both the similarities and the differences it has with 1xEV-DO. Nevertheless, the fact that LTE and 1xEV-DO concepts can be laid out side-by-side in this way should help to reassure 1xEV-DO operators that the step from 3G to 4G is not as big a leap as they may have thought.

Award Solutions, Inc. provides exceptional training and consulting in advanced wireless and Internet technologies. Our proven experience enables us to offer a complete suite of services: cutting edge technology training, customized training solutions, and advanced technology consulting. 

Our products and services provide our clients with innovative, flexible, and cost-effective solutions that help rapidly boost their workforce productivity and competence to more quickly meet their market demands. Award Solutions will be happy to customize our course content to meet any specific needs. 

The level of technical depth in our training courses gives students a unique benefit that they can apply immediately. We offer a range of courses appropriate for audiences needing a high-level overview, as well as engineers looking for in-depth details. 

Award Solutions continues to provide successful training and network performance solutions as well as professional consulting services for many telecommunications and Internet equipment manufacturers, service providers and enterprises, just as we have since 1997. 

Please visit our website at www.awardsolutions.com for our full line of services and latest curriculums. 

If you have any questions, concerns or comments regarding this document, please write to us at: friends@awardsolutions.com 

          

 The 3GPP and LTE logos are the property of Third Generation Partnership Project (3GPP). The 3GPP2 logo is property of Third Generation Partnership Project (3GPP2) and its organization partners. The TIA logo is property of Telecommunications Industry Association (TIA). The content of this document is based on 3GPP/LTE, 3GPP2 and TIA specifications which are available at www.3gpp.org, www.3gpp2.org, and www.tiaonline.org.