Cdma2000 1x Protocol Layers and Signaling

cdma2000 1x Protocol Layers and

Signaling

Actix Inc 1851 Alexander Bell Drive Suite 405 Reston, VA 20191 Tel: (703) 740-8900 Fax: (703) 740-8908 Email: [email protected] Web site: http://www.actix.com COPYRIGHT © Actix Inc 2002

cdma 2000 Protocol Layers and Signaling

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Overview of cdma2000 1X...............................................................................3 Benefits of cdma2000 1X ................................................................................3

cdma2000 is an Evolution of cdmaOne (IS-95)..............................................3 Increased Voice Capacity ............................................................................4 Increased Data Transmission Speeds...........................................................5 Improved Terminal Battery Life.....................................................................6

cdma2000 1X Protocols ..................................................................................7 Physical Layer.............................................................................................8

New cdma2000 1X Forward Link Channels................................................9 Common Channels ...............................................................................9 Dedicated Channels............................................................................10

New cdma2000 1X Reverse Link Channels .............................................10 Common Channels .............................................................................11 Dedicated Channels............................................................................11

Medium Access Control Layer....................................................................11 The Multiplex Sub-Layer .....................................................................12

Radio Link Protocol Layer ..........................................................................12 Signaling For Common Tasks........................................................................14

Voice Call Origination ................................................................................15 Data Call Origination..................................................................................16 Voice Call Termination...............................................................................17 Data Call Termination................................................................................18 Soft Handoff..............................................................................................19 Inter-frequency Hard Handoff .....................................................................20


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Overview of cdma2000 1X cdma2000 is the third generation (3G) solution based on IS-95, or more commonly known as cdmaOne, and unlike some 3G standards, it is an evolution of an existing wireless standard. cdma2000 supports 3G services as defined by the International Telecommunications Union (ITU) for IMT-2000. 3G networks will deliver wireless services with better performance, greater cost-effectiveness and significantly more content and cdma2000 technology satisfies those goals.

Both cdmaOne and cdma2000 systems are based on spread spectrum multiple-access technology that has rapidly gained global acceptance by wireless operators. cdmaOne and cdma2000 networks spread coded conversations and data transfers over 1.25 MHz of spectrum, allowing a large number of users to simultaneously share the same carrier.

This first phase of the cdma2000 upgrade (variously called 1XRTT, IMT MC1X, 3G1X, or just plain 1X) is designed to double current voice capacity and support always-on data transmission speeds ten times faster than those typically available today-some 144 kbit/s on both the forward and reverse links. Handset standby times should also increase by up to 50 percent. Users, meanwhile, will be able to benefit from enterprise and consumer applications that would normally require more bandwidth, including personal information management, telemetry, corporate intranet access, videoconferencing, gaming and music on demand.

Benefits of cdma2000 1X The new software in the BSs and BSCs to enable cdma2000 provide a number of key benefits.

cdma2000 is an Evolution of cdmaOne (IS-95) While the cdma2000 specification allows for an evolutionary migration to later advances in cdma2000 that use core IP networks and voice-over-IP, the current 1X migration requires relatively modest hardware and software upgrades to existing cdmaOne infrastructure. Even then, operators can upgrade to 1X without having to implement it throughout their entire cdmaOne network, which means they can upgrade certain hotspots that require voice capacity enhancements or higher data speeds.

cdma2000 can be deployed in existing spectrums such as 1900MHz along with an existing cdmaOne system, overlaying its new feature set and increased capacity on the existing cdmaOne networks. Most importantly, it uses existing (and paid for) 1.25 MHz spectrum.

Handsets using cdma2000 technology will also be backward compatible to the existing cdmaOne networks, so current handsets and features will operate over


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next generation networks providing continued access both at home and while roaming. Operators who deploy 3G with 1X will still have roaming with worldwide CDMA operators on their cdmaOne networks.

The flexible migration from cdmaOne provides a series of upgrades leading to cdma2000's increased voice capacity and Megabit 3G data rates, allowing each operator to upgrade when its individual market requirements dictate without significantly upgrading infrastructure or purchasing new spectrum.

To permit the new services that a 1X implementation promises, cdmaOne operators will have to do some retrofitting of base station channel cards with 1X cards, implement software upgrades in specific areas of their existing networks, and add some new IP-centric boxes to allow them to implement the data/voice 1X specification in part or in full. The approach to this will differ in form depending on what vendor equipment has been chosen, although most vendor approaches include ensuring backward compatibility with existing base stations with flexible future-proofing hooks for new technologies like intelligent antennas to boost capacity.

At the base station level, new channel cards are required to support the increased capacity and enhancement in IP provisioning. New radio control software will also be required in the BS to enable the new channels, and where appropriate, software upgrades will also be necessary for base station controllers. Some operators may, however, want to implement separate boxes in the BSs in parallel with existing cdmaOne cards, primarily for cdmaOne backwards compatibility, and 1X testing imperatives.

Increased Voice Capacity The increase in voice and data capacity stems from advances in modulation algorithms, new IP backbones, and new chipsets that support up to 32 simultaneous users on a single chip, a four-fold increase over the previous generation.

To improve the forward link performance fast power control is used. The improved power control will allow the network to respond more quickly to changes in signal propagation between the base station and the mobile.

Coherent detection will also improve the performance of the reverse link up to 3 dB (100%) compared to non-coherent reception used by the second generation CDMA system. To facilitate coherent detection a new, mobile originated pilot signal is required (Reverse Pilot Channel). This pilot signal is very similar to the one that is transmitted by a cdmaOne base station resulting in coherent reception on the forward link.


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Increased Data Transmission Speeds The cdma2000 standard is evolving to continually support new services in a standard 1.25 MHz carrier. cdma2000 1X will deliver average data rates of 144 kbps. Phase two - labeled cdma2000 1xEV - will provide for data rates greater than 2 Mbps.

Peak, symmetrical data rates of 153.6kbit/s in ideal conditions are possible, but field trails suggest that, as this is a shared resource, 130kbit/s average aggregate throughput is more likely. This will be shared by many users, which could decrease available bandwidth to individual users, much like heavy usage on an office LAN chocks individual demand. However, since usage scenarios suggest the likelihood of more bursty-type 'surfing' where all of the available bandwidth is not swallowed up in one gulp by a few users, fairly high throughputs nearing 130kbit/s are possible for individual users.

To provide secure and efficient transport for wireless data, infrastructure providers have introduced a data delivery mechanism using the PCN. The PCN network is comprised of the Packet Data Serving Node (PDSN) and the Authentication, Authorization and Accounting server (AAA). A Home Agent (HA) can be added to provide Mobile IP-based packet data services.

These new components-which will exist in parallel with the IWF-include the PCF (packet control function) to act as an interface to the MSC and to the PDSN (packet data service node), another new 1X addition. The PDSN is a wireless-savvy router that acts as an interface to the internet and intranets.

Another new addition is the AAA (accounting, authentication and authorization) node which hangs off the PDSN to provide service profiles of end-user-specific data for packet data operations. The PCF was designed to allow the AAA and PDSN to be as off-the-shelf as possible as to ensure interoperability, and to allow a smooth transition to 3G services.


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Figure 1 - cdma2000 1x Network Components

Improved Terminal Battery Life With a cdma2000 1X Terminal (handset, handheld, etc.), users will be able to benefit from enterprise and consumer applications requiring more bandwidth, including personal information management, telemetry and GPS navigation, corporate intranet access, video conferencing, gaming and music on demand.

In order for users to benefit fully from these applications, battery life improvements were required to provide users with reasonable on-air and standby times.

Initial tests indicate that cdma2000 Handset standby times will increase by up to 50%. This improvement results from the addition of the Quick Paging Channel (QPCH) on the forward link. The Quick paging channel provides the mobile with a more efficient mechanism for “listening” to the network when it is idling.


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cdma2000 1X Protocols In an effort to create a more layered approach to the protocol stack in cdma2000, functionality was aligned according to the OSI modeling put forth by the International Standards Organization (ISO). The OSI are:

• Application: user access to OSI environment

• Presentation: translates application information to syntax for data communications

• Session: provides control for application-level peer-to-peer communications; responsible for establishing, maintaining, and terminating connections between peer entities

• Transport: provides sufficiently reliable transportation of data between peer entities

• Network: corresponds to underlying network (e.g. wireless network) over which packets from transport layer are transmitted; has own connection establishment and maintenance procedures

• Data link: provides sufficiently reliable transportation of network-level packets over physical layer

• Physical: actual transmission pipe over which raw data flows (e.g. microwave link in wireless network)

This type of layering model is difficult to implement in wireless networks due to functions requiring several layers to coordinate with each other. For instance, in a wireless system, the network layer may be in charge of radio resource control; however, that functionality cannot be totally independent from the physical layer due to functions such as soft handoff. Nevertheless, cdma2000 was structured to include layering for the network layer and below. The basic cdma2000 layers and their corresponding OSI layers are:

• Layer 3 signaling, packet data services, voice data - OSI Network layer and up

• Link Access Control (LAC) - OSI Data link layer

• Medium Access Control (MAC) - OSI Data link layer

• Physical layer - OSI Physical layer


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Figure 2 - cdma2000 1x Protocol Layers

The following sections will describe the basic cdma2000 layers.

Physical Layer The cdma2000 physical layer retains backwards compatibility not only to leverage IS-95 equipment development but to also provide a smooth upgrade path for cellular operators. In this way, cdma2000 systems could be gradually phased into existing IS-95 networks without disrupting service. As a result, many mechanisms such as reverse link power control and soft handoff remain essentially the same from the physical layer standpoint.

The cdma2000 physical layer classifies different modes of operation into radio configurations (RC's) for both the forward and reverse links. For instance, Radio Configurations 1 and 2 (RC1 and RC2) are the Rate Set 1 and Rate Set 2 modes of operation respectively in IS-95. However, radio configurations greater than 2 define new modes of operation in cdma2000.

Several new channels exist for cdma2000 1X in order to support the new modes of operation.


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New cdma2000 1X Forward Link Channels

Figure 3 - cdma2000 1x Forward Link Channels

Common Channels F-CCCH - Forward Common Control Channel and

F-BCCH – Forward Broadcast Control Channel

The forward common control channel (FCCCH) and forward broadcast control channel (FBCCH) may be used for carrying common signaling much like the paging channel. These channels may be used specifically for cdma2000 mobiles, thus relieving some of the overhead on the paging channel.

F-CAPICH – Forward Common Auxiliary Pilot Channel

The forward common auxiliary pilot channel (F-CAPICH) is used to assist in spot coverage and transmit diversity applications. The Walsh code assignment for an auxiliary pilot can be of length 128, 256, or 512.

F-QPCH – Forward Quick Paging Channel

The forward quick paging channel (FQPCH) is an on-off keyed (OOK) indicator to the mobile to wake up for a message on the paging channel. This is useful for conserving battery life in the mobile when it is idling.

F-CPCH – Forward Common Power Control Channel

For new access modes on the reverse link, a forward common power control channel (FCPCH) exists in which users’ power control bits may be slotted in time.


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Dedicated Channels cdma2000 1X introduces the forward dedicated common control channel (FDCCH) and forward supplemental channel (FSCH) in addition to the forward fundamental channel (FFCH) previously used for voice and signaling.

F-DCCH – Forward Dedicated Common Control Channel

The FDCCH may be used primarily for signaling and can be used for other high priority (non-voice) traffic such as retransmissions for data protocols.

F-SCH – Forward Supplemental Channel

The FSCH is strictly for data traffic, and can take much higher rates than an IS-95 compatible forward supplemental code channel. Each forward traffic channel contains up to two supplemental channels.

F-FCH – Forward Fundamental Channel

The forward fundamental channel (FFCH) is still primarily for voice, but can be used for low rate data transmission as in IS-95 networks.

New cdma2000 1X Reverse Link Channels

Figure 4 - cdma2000 1x Reverse Link Channels


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Common Channels R-CCCH – Reverse Common Control Channel and

R-EACH – Reverse Enhanced Access Channel

The reverse common control channel (RCCCH) and reverse enhanced access channel (REACH) were introduced to provide more reliable access by means of slotting different users before they transmit bursts on the reverse link and to provide a coherent form of reception for the base station access probe receiver. In addition, some burst data services that were not possible over the IS-95 access channel could be accommodated using these features.

Dedicated Channels R-PICH – Reverse Pilot Channel

The RPICH was introduced to provide coherent reverse link detection and fast forward link power control.

R-FCH – Reverse Fundamental Channel and

R-SCH – Reverse Supplemental Channel and

R-DCCH – Reverse Dedicated Common Control Channel

Except for the RPICH, the types of data associated with each channel are identical to their forward link counterparts.

Medium Access Control Layer cdma2000 introduced a MAC specification in an effort to ensure a correspondence between itself and the OSI layering model for data services.

It receives its payload either from the link access control (LAC) layer or directly from one or more data services, provides the necessary functionality for multiplexing these different types of payload onto the physical layer, and describes to an extent some aspects of the operation of the access modes for the cdma2000 reverse link.

The cdma2000 MAC layer provides two important functions:

• Best Effort Delivery - reasonably reliable transmission over the radio link with a Radio Link Protocol (RLP) that provides a “best effort” level of reliability; and

• Multiplexing and QoS Control - enforcement of negotiated QoS levels by mediating conflicting requests from competing services and by the appropriate prioritization of access requests.


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The Multiplex Sub-Layer The multiplex sub-layer has both a transmitting and a receiving function. The multiplex sub-layer transmitting function combines information from various sources (e.g., Upper Layer Signaling, Data Service instances, and Voice Service) and forms Physical Layer SDUs for transmission. The multiplex sub-layer receiving function separates the information contained in Physical Layer SDUs, and directs the information to the correct entity (e.g., Upper Layer Signaling, Data Service instances, or Voice Service).

Figure 5 - The Multiplex Sub-Layer

Radio Link Protocol Layer The conventional internet protocol (IP) stack, which is used for wire-line data communications, tends to suffer when used over a wireless cellular environment. This is because IP-protocols generally rely on one layer of reliability, the transmission control protocol (TCP), which serves to recover lost octets based on ARQ methods. TCP is optimized for wire-line networks; cellular networks, which generally suffer higher error rates and are subject to tighter bandwidth restrictions, cannot provide the basic performance needed for even TCP to be sufficient for error recovery. Moreover, some real-time applications that may be run at higher error rates but cannot sustain the delay of TCP octet recovery may instead use the universal datagram protocol (UDP). UDP has no means of recovering packets lost over the wireless network.

As a result, wireless systems use radio link protocols (RLP’s) to provide an additional layer of reliability on top of TCP. RLP does not accept IP packets


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directly in IS-95/cdma2000. Instead, IP packets are passed through a point-to-point protocol (PPP) instance. PPP serves primarily to provide some security to the IP datagrams. RLP therefore must be able to segment PPP packets for transmission, and reassemble received RLP PDU’s into whole packets for delivery to the PPP layer.

RLP provides reliability by means of ARQ. This means that RLP PDU’s are retransmitted only when the receiver specifically requests them. This type of ARQ is also sometimes referred to as a NAK-based protocol.

If the receiver sends a NAK for a missing RLP PDU, it must initiate a timer for that RLP PDU (the retransmission timer). This timer, which is only incremented upon the receipt of valid RLP PDU’s, cannot exceed a certain pre-established number (based on the expected round trip time RTT for a retransmission). This timer is terminated once the retransmission is received correctly. Otherwise, once this timer has expired, the receiver may send another NAK and start another timer known as the abort timer (also based on the RTT). If the abort timer expires, then the RLP receiver gives up and passes whatever correct octets it has received in the PPP packet up to the PPP layer. In this manner, RLP can provide some limited error recovery for data packets in the wireless channel, but it does not provide excessive reliability so that upper layers may erroneously determine that the underlying connection has been lost.

When the receiver has detected a missing RLP PDU, or a timer has expired so that a NAK must be re-sent, RLP may send more than one NAK as a result. The maximum number of timer events for the recovery of an RLP PDU is also sometimes referred to as the number of NAK rounds allowed. There are a maximum number of NAK’s per round as well.

cdma2000 has provided a means of negotiating the levels of reliability at the RLP layer during the initialization of the data service. More precisely, the NAK’s per round and maximum number of rounds may be negotiated at the beginning of the call.


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Signaling For Common Tasks To fully understanding the protocol layering model used in cdma2000, it is useful to see how common network tasks are completed and how each network element contributes to the process. The tables in this section describe the message flow for common sets of signaling. These signaling diagrams come from the “Interoperability Specification (IOS) for CDMA 2000 Access Network Interfaces (PN-4545)”. The IOS can be used as an additional reference for cdma2000 1x signaling procedures.

Figure 6 - Signaling in a cdma2000 1x Network

Um Interface – The connection between the BTS and the mobile (the Air Interface)

A Interface – The connection between the BSC and the MSC

Ater Interface – The connection between BSCs to support soft/softer hand-off processes

Aquinter Interface – The connection between the PCF and the BSC

Aquater Interface – The connection between the PDSN and the PCF

Um Interface – The connection between the BTS and the mobile (the Air Interface)

A Interface – The connection between the BSC and the MSC

Ater Interface – The connection between BSCs to support soft/softer hand-off processes

Aquinter Interface – The connection between the PCF and the BSC

Aquater Interface – The connection between the PDSN and the PCF


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Voice Call Origination The event pictured below describes a basic mobile station origination in the system. Though only the basic process is pictured here, an origination may incorporate additional procedures, such as an Access Probe Handoff, Access Handoff and/or Channel Assignment into Soft/Softer handoff.

Figure 7 - Voice Call Origination


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Data Call Origination This example shows the activation of a packet data call.

Figure 8 - Data Call Origination


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Voice Call Termination This example shows the system signaling for a voice call termination.

Figure 9 - Mobile Termination for Voice Call


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Data Call Termination This example shows a data call termination as the result of a power down operation by the mobile.

Figure 10 - Data Call Termination


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Soft Handoff This example shows the signaling for the addition of a PN during soft (or softer) handoff.

Figure 11 - Soft Handoff Signaling


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Inter-frequency Hard Handoff This example shows the signaling for a successful hard handoff event.

Figure 12 - Inter-frequency Hard Handoff

Cdma2000 1x Protocol Layers and Signaling

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