Category: UMTS

HSPA+ Background Information

It looks like UMTS will not give way to LTE in the future just like that. The High Speed Packet Access (HSPA) extensions which are now used in most UMTS networks today might get another upgrade in the future with HSPA+. Features such as 64QAM modulation, MIMO and Continuous Packet Connectivity (CTC) are on the horizon. Here are some documents I found recently which go a bit deeper into the topics:

Enjoy!

T-Mobile Starts Using DSL for 3.5G HSPA Backhaul

Unstrung recently reported that T-Mobile has started to deploy RAD’s Ethernet over DSL solution for backhauling 3.5G traffic from their UMTS / HSPA base stations. I wondered in the past how soon we would see something like this happening since current 2 MBit/s E-1 line rental costs are prohibitively high and several are required for the bandwidth requirements of a 3.5G base station. The article says deployment starts in Germany, where T-Mobile is the incumbent and has surely made a favorable deal with their fixed line branch, T-Com, who is in the process of deploying a VDSL overlay network besides the already existing ADSL/ADSL2+ network. As VDSL only works over short distances, T-COM deploys curbside VDSL cabinets every several hundred meters. With 52 MBit/s in downlink and 11 MBit/s in uplink, a VDSL link offers more than enough bandwidth for a base station with multiple sectors. Backhaul from the cabinet is also not a problem since they are connected to the core network by fiber. The article doesn’t say if the base station continues to use E-1 links for voice traffic or if all data is backhauled via the DSL link.

Light Reading Webinar on Mobile Backhaul Evolution

With mobile networks getting faster and faster a growing pain for network operators is the backhaul connection between the base station sites and the next element in the network. Today, T-1 or E-1 connections are used with a line rate of 1.5 and 2 MBit/s. With HSDPA being put in place today,  backhaul capacity requirements of 3G base stations now reach 10 MBit/s or more. This means putting additional T-1 or E-1 lines in place. While this might still work today for HSDPA speeds despite the associated rising costs it certainly won’t work tomorrow for WiMAX, LTE and other Beyond 3G technologies that require backhaul capacities of 60 MBit/s per base station and more.

So the big question is what comes after T-1/E-1 connections over copper, fiber or microwave!? The common answer these days seems to be:

IP over Ethernet with the capability to carry legacy GSM (TDM) and UMTS/HSDPA (ATM) links in IP pseudo-wires alongside native IP traffic generated by native WiMAX and LTE base stations.

But how do you connect the base station sites to Carrier Ethernet Networks? Can the last mile be done over copper, is fiber required or is next generation microwave an alternative? Questions over Questions 🙂

I found some answers in a recent one hour Light Reading Webinar on the topic which is available for free at this link. If you are interested in the topic take a look.

Femtocell Thoughts – Part 3

In part one of this miniseries on femtocells I’ve been looking at
the benefits for mobile operators and part two covered the question why users would
put a femtocell into their home. This final part looks at the technical background and hurdles and gives a conclusion.

In practice it is extremely important to integrate femtocells with DSL or cable modems for several reasons. First, femtocells are installed by the user and such an approach therefore ensures that the installation is easy and is done properly.

Additionally, an integrated device is the only way to ensure quality of service for the femtocell since data traffic generated by 3G voice calls must be prioritized on the fixed line link over any other traffic. If a femtocell was attached to an already existing DSL or cable router which already serves other users, uplink data traffic of these users could severely impact 3G voice calls since ordinary DSL or cable routers do not have quality of service (QoS) features to ensure that traffic from the femtocell is prioritized. This behavior can already be observed in practice today in other situations. If an ordinary DSL or cable router is used for a VoIP call in addition to a simultaneous file upload, voice quality is usually very bad due to the packet delay and insufficient bandwidth availability caused by the file transfer.

Thus, a mobile operator deploying femtocells ideally owns DSL or cable access as well or is at least partnering with a company owning such assets. This way a single fixed line gateway could be deployed with Wifi for PCs and other devices and a femto radio module for 3G mobile devices. The single phone per user idea also benefits from such an approach since owning or partnering for DSL or cable access removes the competition between fixed and wireless voice. This also ensures that a femtocell is only used in locations where the mobile operator has licenses to operate femtocells since they use licensed 3G frequency bands.

In practice it can be observed today that a number of mobile operators are taking this route already by either buying DSL access provider companies or at least partnering with them (e.g. Vodafone/Arcor or O2/Telefonica in Germany). It’s unlikely that this is done specifically to roll out 3G femtocells at a later stage but it seems that such companies have understood that it is vital for the future of a telecommunication company to have both wireless and fixed assets in order to stand a chance to be more than a mere bit-pipe for services running over the network. On a side note it is interesting to see the trend of splitting up fixed and mobile access into separate companies several years ago seems to revert now and pains of separation are now followed by pains of re-unification.

Another technical aspect concerning femtocells is interference. In 3G networks, cells usually all transmit on the same frequency and interference is managed by having enough space between them and by adjusting output power and antenna angles. Most 3G operators have at least two frequencies they can use so femtos could for example use the mostly unused second frequency. However, there is still an issue with interference between femtocells of users which live in the same apartment building and have thus installed their equipment close to each other. Left on its own this will result in lower capacity of each cell and might impact quality of service.

Conclusion

When looking at the arguments presented above, femtocells are not likely to be an immediate and outright success. A number of hardware evolutions will probably be needed before form factor, usability and quality of service are adequate. This is likely to take a couple of years. Also, mobile operators need to continue their path of buying or partnering with companies owning fixed line DSL or cable access. This will surely also not happen overnight. However, there is currently still enough capacity available in the macro layer of the network so femtocells are not immediately needed to reduce the load on the network. Therefore, the major immediate benefit of femtocells is improving in-house coverage especially in rural regions, which thus remains a niche market for now, since 2G and 3G coverage and capacity for urban users is usually sufficient for in-house coverage. As such the story of femtocells might parallel the evolution of UMA (Universal Mobile Access) which has similar goals but a completely different concept. That’s a story for another day however…

As always, comments are welcome.

Femtocell Thoughts – Part 2

In part one of this miniseries on femtocells I’ve been looking at the benefits for mobile operators. This part deals with why users would put a femtocell into their home.

From the user’s point of view the advantages of femtocells are less clear to me. While the user shares all of the operator advantages discussed in a previous blog entry, increasing customer retention and thus churn is not necessarily in the interest of users since it could reduce competition. Also, it is unlikely that all family members use the same mobile operator and thus could benefit from a single femto cell.

In addition, mobile multimedia users are usually still early adopters which tend to use sophisticated phones, of which many include Wifi. With such phones a femto cell for multimedia content is not required since Wifi offers a similar or better experience for Internet content. Multimedia services offered by mobile network operators, however, are usually not available over Wifi which, from the end user perspective, is not a huge loss since early adopters tend to use Internet services rather than multimedia services of operators that are usually more expensive or come with limitations not acceptable to such users.

An advantage not mentioned before is that better 3G in-house penetration would increase call establishment success rate for 3G video calls since mobiles reselecting to the 2G network because reception quality is better can not be used for incoming or outgoing video calls. Thus, femtocells could become an important element in the future to make video calls more popular as the service still fights with the famous hen/egg problem of 3G network availability and number of users with compatible handsets.

Monetary incentives could persuade users to install femto cells. Operators could for example offer cheaper prices for voice calls that are handled via the femto cell. Also, the operator could propose to share revenue with femto ‘owners’ if other subscribers use the cell for voice and data communication instead of a macro cell.

Often the argument is brought forward that femtocells allow to market single phone solutions in which the user no longer has a fixed line phone and uses his mobile phone both at home and on the go. However, such solutions which use the macro layer instead of femtocells have already been available for several years in countries such as Germany (O2’s famous home zone for example) and are already very popular. Also, it is unlikely that mobile network operators would have competitive prices for all types of calls so many users would still use a SIP phone or software client on a PC for such calls at home. Calling a mobile number is still more expensive in most parts of the world excluding the U.S.A. than calling fixed line phones so single phone offers have to include a fixed line number for the mobile phone in order. Again, this is already done in practice for example by O2 in Germany for a number of years but femtocells might enable the mobile network operator to deliver such services cheaper than how it is currently done over the macro layer.

It should alsobe mentioned that using a femtocell would have a configuration and usability advantage over SIP Wifi phones. However, it is likely that the configuration process for SIP and Wifi on handsets will improve over the next few years thus decreasing this advantage.

To be continued

So much for now on the user’s point of view on femtocells. In the third part, to come soon, I will take a look at the technical background and hurdles.

As always, comments are welcome!

Femtocell Thoughts – Part 1

There is currently a lot of hype around Femtocells, tiny user installable 3G cells for homes and offices. Surely an interesting technical concept but still with many question marks attached such as why would users want a 3G cell at home or at the office and what the benefits are for the operator. Here’s what I think:

Operator Benefits

3G networks are operated on the 2100 MHz frequency band in Europe and Asia and in the 1900 MHz band in the U.S. which is far from ideal for in-house coverage. Even in cities it can be observed that dual mode 2G/3G mobiles frequently attach to the 2G network because many GSM operators use the 900 MHz band in Europe which is much better suited for in-house coverage as lower frequencies penetrate walls much better. Some proponents of Femtocells claim that in-house coverage for voice calls are greatly improved by Femtocells. In cities however, this benefit is rather small since GSM in-house coverage is usually not an issue. The user on the other hand does not really care if his voice call is handled by the 2G or 3G network.

An improvement could be seen however in cases where the mobile can’t decide to stick with either the 2G or the 3G network due to changing 3G signal levels. This creates small availability outages while the mobile selects the other network type. During these times, incoming voice calls are either rejected or forwarded to voicemail.

Also, it can often be observed in practice that a mobile device with weak 3G in-house coverage changes to the 2G network once a connection to the Internet is established (e.g. to retrieve eMails or to browse the web on the mobile phone) and sometimes changes back to the 3G network during the connection. The reason for these ping pong network selections are the changing reception levels due to the mobility of the user and changing environmental conditions. Such network changes result in outage times which the user notices since an eMail takes longer to be delivered or because it takes a long time for a web page to be loaded.

Another solution to the issues described above is the use of the 900 MHz frequency band for 3G in Europe and Asia and the 850 MHz band in the U.S. It is likely that this will happen over the next few years since regulators more and more tend to open the 900 MHz band for 3G networks in Europe. It will take a number of years however before network operators will have deployed their 3G networks in those lower frequency ranges and until devices for these bands are available. It’s also likely that 900 MHz cells would first be used to cover rural areas instead of enhancing coverage in areas already covered by 3G in the 2100 MHz band. In the meantime, Femtocells definitely have the advantage.

As the above weaknesses of 3G in higher frequency bands show, femtocells can increase customer satisfaction. Putting a femtocell in the user’s home would have the additional advantage for network operators of reducing churn, i.e. customers changing contracts and changing the network operator in the process. Customer retention is all the more reinforced if the Femto comes in a bundle with DSL access as further described below since changing wireless contracts also has consequences for the fixed line Internet access at home.

Another advantage of femtocells is to reduce the gradual load increase on the 3G macro network as more people start using 3G terminals for voice and data connections. This could result in a cost benefit since if the right balance of macro and femtocells are reached, fewer expensive macro cells would be necessary to handle overall network traffic.

The question is how much these advantages are worth to a network operator since Femtocells do not come for free!?

More to come

So much for now. Part 2 to come soon deals with why users would put a 3G femotcells into their home and part 3 will look at the technical background and hurdles for femtocells.

As always, comments are welcome!

Continuous Packet Connectivity (CPC) Is Not Sexy – Part 3

In a previous post I’ve given a broad overview of a 3GPP release 7 work item called "Continuous Packet Connectivity" (CPC).
This feature or rather this set of features aim to improve user
experience by enhancing battery lifetime, reaction time after idle
times and to increase network bandwidth in situations with many
simultaneous voice over IP and other real time service users. Rather
than introducing a bold new concept, CPC very much works "under the
hood" by improving functions that are already present. Part 2 of this mini series has started to look at a first set of features and this part now finishes by looking at the remaining ones:

Discontinuous reception (DRX) in Downlink at the UE (based on section 4.5 of 3GPP TR 25.903):

While a mobile is in activate high speed (HSDPA) mode it has to monitor one or more high speed shared control channels (HS-SCCH) to see when packets are delivered to it on the high speed shared channels. This monitoring is continuous, i.e. the receiver can never be switched off.

For situations when no data is transmitted or the average data transfer rate is much lower than what could be delivered over the high speed shared channels, the base station can instruct the mobile to only listen to selected slots of the shared control channel. The slots which the mobile does not have to observe are aligned as much as possible with the uplink control channel gating (switch off) times. Thus there will be times when the terminal can power down the transmitter unit to conserve energy.

Once more data arrives from the network than what can be delivered with the selected DRX cycle the DRX mode is switched off again and the network can once again schedule data in the downlink continuously.

HS-SCCH-less operation which includes an HS-SCCH less initial transmission  (based on section 4.7 and 4.8 of TR 25.903):

This feature is not intended to improve battery performance but to increase the number of simultaneous real time VoIP users in the network.

VoIP service e.g. via IMS requires relatively little bandwidth per user and thus the number of simultaneous users can be high. On the radio link, however, each connection has a certain signaling overhead. Thus, more users mean more signaling overhead which decreases overall available bandwidth for user data. In the case of HSDPA, the main signaling resources are the high speed shared control channels (HS-SCCH). The more active users, the more they proportionally require of the available bandwidth.

HS-SCCH-less operation aims at reducing this overhead. For real time users which require only limited bandwidth, the network can schedule data on high speed downlink channels without prior announcements for the terminal on a shared control channel. This is done as follows: The network instructs the mobile not only to listen to the HS-SCCH but in addition to all packets being transmitted on one of the high speed downlink shared channels. The terminal then attempts to blindly decode all packets received on that shared channel. To make blind decoding easier, packets which are not announced on a shared control channel can only have one of four transmission formats (number of data bits) and are always modulated using QPSK. These restrictions are not an issue for performance since HS-SCCH-less operation is only intended for low bandwidth real time services.

The checksum of a packet is additionally used to identify for which terminal the packet is intended for. This is done by using the terminal’s MAC address as an input parameter for the checksum algorithm in addition to the data bits. If the terminal can decode a packet correctly and if it can reconstruct the checksum the packet is intended for the terminal. If the checksum does not match then either the packet is intended for a different terminal or a transmission error has occurred. In both cases the packet is discarded.

In case of a transmission error the packet is automatically retransmitted since the terminal did not send an acknowledgement (HARQ ACK). Retransmissions are announced on the shared control channel which requires additional resources but should not happen frequently as most packets should be delivered properly on the first attempt.

And for more on HSDPA and HSUPA…

I hope that this introduction to Continuous Packet Connectivity (CPC) answers more questions than it raises. In case some fundamental things remain unclear consider taking a look at my book on mobile communication systems which covers HSDPA and HSUPA from the ground up.

Continuous Packet Connectivity (CPC) Is Not Sexy – Part 2

In a previous post I’ve given a broad overview of a 3GPP release 7 work item called "Continuous Packet Connectivity" (CPC). This feature or rather this set of features aim to improve user experience by enhancing battery lifetime, reaction time after idle times and to increase network bandwidth in situations with many simultaneous voice over IP and other real time service users. Rather than introducing a bold new concept, CPC very much works "under the hood" by improving functions that are already present. Part 2 and 3 of "CPC Is not sexy" now take a closer look at the individual features:

A new UL DPCCH slot format configurable by Layer 3 in a semi-static way (Section 4.1 of 3GPP TR 25.903):

In UMTS networks, information is sent in both uplink and downlink in virtual channels. For a connection several channels are used simultaneously since there is not only user data sent over a connection but also control information to keep the link established, to control transmit power, etc. Currently, the radio control channel in uplink (the Uplink Dedicated Control Channel, UL DPCCH) is transmitted continuously even during times of inactivity in order not to loose synchronization. This way, the terminal can resume uplink transmission of user data without delay whenever required.

The channel carries four parameters (for details, see 3GPP 25.211, chapter 5.2.1):

  • Transmit power control (TPC)
  • Pilot (Used for channel estimation of the receiver)
  • TFCI (Transport Format Combination Identifier)
  • FBI (Feedback indicator)

The pilot bits are always the same and allow the receiver to get a channel estimate before decoding user data frames. While no user data frames are received, however, the pilot bits are of little importance. What remains important is the TPC. The idea behind the new slot format is to increase the number of bits to encode the TPC and decrease the number of pilot bits while the uplink channel is idle. This way, additional redundancy is added to the TPC field.

As a consequence the transmission power for the control channel can be lowered without running the risk of corrupting the information contained in the TPC. Once user data transmission resumes, the standard slot format and higher transmission power is used again.

UL HS-DPCCH gating/discontinuous transmission (DTX) in 2 cycles (based on section 4.2 of TR 25.903 ) connected with a F-DPCH gating in DL and an implicit CQI reporting reduction in UL (see section 4.4 of TR 25.903)

CQI reporting reduction: To make the best use of the current signal conditions in downlink, the mobile is required to send information back to the network about how well a transmission was received. The quality of the signal is reported to the network with the Channel Quality Index (CQI) alongside the user data in uplink. The proposed concept has the goal to reduce the transmit power of the terminal while data is transferred in the uplink but not in the downlink by reducing the CQI reporting interval.

UL HS-DPCCH gating (gating=switch off): When no data is transmitted in both uplink and downlink the UL DPCCH for HSDPA is switched off. Periodically it is switched on for a short time to transmit bursts to the network in order to maintain synchronization. This improves battery life for applications such as web browsing. The solution can also improve battery consumption for VoIP and reduces the noise level in the network (i.e. more simultaneous VoIP users)

F-DPCH gating: Terminals in HSDPA active mode always receive a Dedicated Physical Channel in downlink in addition to high speed shared channels which carries power control information and Layer 3 radio resource (RRC) messages, e.g. for handovers, channel modifications etc. The Fractional-DPCH feature puts the RRC messages on the HSDPA shared channels and the mobile thus only has to decode the power control information from the DPCH. At all other times the DPCH is not used by the mobile (thus it’s fractional). During these times, power control information is transmitted for other mobiles using the same spreading code. Consequently, several mobiles use the same spreading code for the dedicated physical channel but listen to it at different times. That means that fewer spreading codes are used by the system for this purpose which in turn leaves more resources for the high speed downlink channels.

Your head is still not spinning? Great, then watch out for part 3 of this mini-series which explains UE DRX and HS-SCCH-less reception!

If WiMAX Becomes a 3G (IMT-2000) Standard, What’s Left for 4G?

Now that 3G systems such as UMTS are under full deployment, the industry is looking forward to what comes next. While some say that WiMAX is a 4G system, the IEEE and the WiMAX forum think that 802.16e is rather a 3G technology and have asked the ITU (International Telecommunication Union) to include this standard into its IMT-2000 specification (International Mobile Telecommunications 2000). This specification is generally accepted as being the umbrella defining which standards are to be considered 3G.

This is mainly a political move since in many regions of the world, frequencies are reserved for 3G IMT-2000 systems. If WiMAX were included in IMT-2000, and it looks like it will be in the near future, some frequency bands such as the 2.5 GHz IMT-2000 extension band in Europe could be used for WiMAX without changing policies.

So what remains for IMT-Advanced, the ITU umbrella name for future 4G technologies?

Currently there is still no no clear definition by ITU of the characteristics of future 4G IMT-Advanced systems. The ITU-R M.1645 recommendation gives first hints but leaves the door wide open:

It is predicted that potential new radio interface(s) will need to support data rates of up to approximately 100 Mbit/s for high mobility such as mobile access and up to approximately 1 Gbit/s for low mobility such as nomadic/local wireless access, by around the year 2010 […]
These data rate figures and the relationship to the degree of mobility (Fig. 2) should be seen as targets for research and investigation of the basic technologies necessary to implement the framework. Future system specifications and designs will be based on the results of the research and investigations.

When WiMAX is compared to the potential requirements above it’s quite clear that the current 802.16e standard would not qualify as a 4G IMT-Advanced standard since data rates even under ideal conditions are much lower.

3GPP’s Long Term Evolution (LTE) project will also have difficulties fulfilling these requirements. Even with the recently proposed 4×4 MIMO, data rates in a 20 MHz carrier would not exceed 326 MBit/s. And that’s already a long stretch since putting 4 antennas in a small device or on a rooftop will be far from simple in practice. If WiMAX is accepted as a 3G IMT-2000 technology, how can LTE with a similar performance be accepted as a 4G IMT-Advanced technology?

Additionally, one should also not forget that IMT-2000 systems such as UMTS are still evolving. UMTS is a good example. With HSDPA and HSUPA, user speeds now exceed the 2 MBit/s which were initially foreseen for IMT-2000 systems. But development hasn’t stopped here. Recent new developments in 3GPP Release 7 and 8 called HSPA+, which will include MIMO technology and other enhancements, will bring the evolved UMTS technology to the same capacity levels as what is currently predicted for LTE on a 5 MHz carrier. HSPA+ is clearly not a 4G IMT-Advanced system since it enhances a current 3G IMT-2000 radio technology. Thus, HSPA+ categorized as a ‘enhanced IMT-2000 system’.

Maybe that’s the reason why the IEEE 802.16 working group is already looking forward and has started work on 802.16m with the stated goal of reaching top speeds of 1 GBit/s.

When looking at current research it’s clear that the transmission speed requirements described in ITU-R M.1645 can only be achieved in a frequency band of 100+ MHz. This is quite a challenge since such large bands are few. Thus, I have my doubts whether these requirements will remain in place for the final definition of 4G IMT-Advanced.

Does It Really Matter If A Technology Is 3.5G, 3.9G or 4G?

While discussions are ongoing the best one can do is to look at HSPA+, WiMAX, LTE and other future developments as "Beyond 3G" systems. After all, from a user point of view it doesn’t  matter if a technology is IMT-2000, Enhanced IMT-2000 or IMT-Advanced as long as data rate, coverage and other attributes of the network can keep up with the growing data traffic.

A whitepaper produced by 3G Americas has some further thoughts on the topic.

As always, comments are welcome!

Continuous Packet Connectivity (CPC) Is Not Sexy – Part 1

Currently, the 3GPP Standards body is giving the final touches to a set of features which are together referred to as Continuous Packet Connectivity (CPC). Several papers mention CPC but I haven’t found a single one so far who could really tell in simple words why these features are necessary and what they actually do. The reason for this is simple: While features like MIMO, spatial multiplexing, beamforming, etc. etc. are broad new concepts (and sound sexy…) CPC consists of a couple of deeply embedded features enhancing existing functionality. Twisting a couple of bits here and a couple of bits there is not very sexy and also not very understandable out of the box.

The Situation Today

With HSPA (HSDPA and HSUPA), mobile devices now have a multi megabit data bearer to both send and receive their data. As devices do not send data all the time there are the following activity states which require more or less interaction with the network:

  • Active: In this mode, the mobile uses HSDPA High Speed Downlink Shared Channels (HS-DSCHs) and an HSUPA Dedicated Uplink Channel (E-DCH).
  • During Short Periods of Inactivity (< around 10s): The network keeps the high speed channels in both uplink and downlink direction in place so the mobile can resume transferring data without delay. Keeping the high speed channels in place means that the mobile has to keep transmitting radio layer control information to the network which has a negative impact on battery life and also decreases the bandwidth for other devices in the cell. 10 seconds is certainly a compromise which is not always ideal since during a web browsing session, for example, it takes the user longer in many cases than this time to click on a new link.
  • During longer periods of inactivity (< around 30s): When no data is transfered for longer than a couple of seconds, the network puts the device on slow channels (RACH in uplink , FACH in downlink). This has the advantage that the mobile does not have to send radio layer control information back to the network anymore. This saves battery capacity to some extent. However, the mobile still has to observe the downlink channel to catch incoming data transmissions which also requires some energy. If the mobile wants to resume communication or in case data arrives for the device from the Internet, the network starts sending/receiving the data on the slow channels and starts a procedure to put the device back on the fast channels. However, this procedure takes in the order of 1 to 2 seconds so the user notices a delay when requesting a new web page for example. This delay is quite undesired.
  • Even longer periods of inactivity (> around 30 seconds): After about 30 seconds, or 60 seconds in some networks, the Radio Network Controller decides that it’s unlikely that the mobile will send or receive any more data for some time and thus puts the connection in Idle state. In this state the mobile does not have to send control information to the network and also does not have to listen to downlink transmissions except during periodic slots in which paging messages are broadcast. These paging messages are important to inform devices of incoming calls or of new data packets. For most of the time the mobile can now completely switch of the receiver and only activate it to receive paging messages and to scan for other cells of the network. If the mobile wants to transmit data again the radio layer has to request a channel again from the network. This takes even longer than the upgrade from a slow channel to a fast channel and results in an even longer delay before a web page starts loading. (Note: I won’t consider Cell-PCH and URA-PCH states for now)

The mobile keeps it’s IP address in all states, i.e. also in Idle state. Therefore, these state changes are  transparent to applications and the user except for the delay when upgrading to a faster channel once data is transfered again.

Desired Improvements

Continuous Packet Connectivity aims at reducing the shortcomings described above by introducing enhancements to keep a device on the high speed channels (i.e. in active state) as long as possible while no data transfer is ongoing by reducing the negative effects of this, i.e. reducing power consumption and reducing the bandwidth requirements for radio layer signaling during that time.

CPC Enhancements

CPC introduces the following new features to reach these improvements:

In Uplink:

  • A new UL DPCCH slot format
  • UL DPCCH gating/discontinuous transmission
  • Implicit CQI reporting reduction

In the Downlink:

  • F-DPCH gating in DL
  • Discontinuous reception (DRX) at the UE
  • A so called HS-SCCH-less operation
  • Modified HS-SCCH for retransmission(s)

Unless you regularly attend 3GPP RAN meetings, this list probably won’t tell you much. But don’t despair, I’ll publish part two of "CPC is Not Sexy" soon in which I will describe these features in understandable terms.