Wireless Network Virtualization LTE case study

Transcription

1 Wireless Network Virtualization LTE case study Yasir Zaki ComNets TZI University of Bremen, Germany April 23 rd, 2010 April 23,

2 Outline Introduction to Wireless Virtualization State-of-the-art LTE Virtualization Motivation, Issues and Proposal Simulation Model and Results Conclusion and Outlook April 23,

3 Introduction to Wireless Virtualization A nature extension from wired to wireless virtualization Virtualization techniques of the wireless medium look for the use of the physical network in a slotted way Virtualization of the wireless resources on the air interface is a scheduling problem of: Tx/Rx power Frequency Time Code Space allocation Time Issue: the wireless links suffer more interference than the wired ones Time April 23,

4 Virtual Radio* Defines a framework for configurable radio networks It extends the network virtualization concept into the wireless domain known as radio virtualization Different virtual radio networks can operate on top of a common shared infrastructure and share the same radio resources It presents how the radio resource sharing can be performed efficiently without interference between the different virtual radio networks * J. Sachs, S. Baucke, Virtual Radio-A Framework for Configurable Radio Networks ; WICON 08, Hawaii, USA, Nov April 23,

5 VANU MultiRAN* Vanu- MultiRAN Virtual Base Station is a commercial software Taking advantage of Vanu software RAN technology, MultiRAN was developed to support multiple virtual base stations (vbts) running on a single BTS hardware platform. The expense of antennas, BTS electronics, and backhaul can all be shared. * J. Chapin; Overview of Vanu Software Radio ; from June April 23,

6 Our LTE Virtualization Proposal April 23, WARD Consortium

7 LTE Virtualization - Motivation For the infrastructure providers: Saving OPEX and CAPEX For the virtual mobile system operators: Lower barrier for the smaller players going to the market Flexibility for network coverage Re-configurability For the end-user: Diversity of services Lower price per bit (?) Others: Power saving in rural areas... April 23,

8 LTE Virtualization - Issues Radio Resource Management (RRM) and Scheduling Inter-operator interference modeling and management Radio Network Planning and Optimization System level evaluation... April 23,

9 LTE Hypervisor The LTE hypervisor is responsible for virtualizing the enb and scheduling the air interface (OFDMA) resources among the Virtual Operators (VOs) The hypervisor collects all relevant information (from all VOs) regarding their users channel conditions, traffic load, VO requirements, VO contracts, etc. Based on these information, the hypervisor tries to allocate the resources to the VO according to what best fits the different requirements April 23,

10 In LTE each operator has his own bandwidth to use LTE Hypervisor cont. Physical enb This Bandwidth will translate into a number of available Physical Resource Blocks (PRBs) This is the smallest unit to be scheduled for a user One PRB consists of 12 subcarriers ~ 180 khz Physical Resources PRBs Channel Conditions The Hypervisor is responsible for allocating the PRBs into the virtual operators enbs Hypervisor (2nd level Scheduler) Virtual enbs The individual virtual enb MAC scheduler will then schedule these PRBs into his own UEs LTE MAC Scheduler LTE MAC Scheduler LTE MAC Scheduler The Hypervisor can make use of the current information to schedule the PRBs: 1. Channel Quality Indicators of UEs (CQI) 2. Buffer Occupancy of UEs 3. Predefined Contracts of the VOPs (bandwidth reservation) 4. Available number of UEs in each VOPs 5. etc. April 23,

11 VNet Operator Contracts The VNet operator will lease resources from the infrastructure provider, this could be done based on predefined contracts The contract specifies the requested resources, i.e. memory, CPU, storage, etc. In addition it specifies the required spectrum to be used by the operator We define mainly four different contract types: Fixed guarantees: the operator requests a fixed bandwidth that would be allocated to it all the time whether it will be used or not Dynamic guarantees: the operator requests a guaranteed maximum bandwidth that would be allocated to the operator if required, otherwise only the actual need would be allocated The operator might only pay based on the used bandwidth which could save cost Best effort with minimum guarantees: the operator specifies a minimum guaranteed bandwidth which will be allocated at all time; and a maximum value that would act as an upper bound. The allocation will be done in a BE manner Best effort with no guarantees: the operator would only be allocated part of the bandwidth if the current load permits i.e. in a pure BE manner April 23,

12 Hypervisor Scheduler In order for the hypervisor to be able to satisfy the operator requests and their predefined contracts, an estimate of the actual needed spectrum of each operator is required The operators need to feedback this estimate value back to the hypervisor (in a predefined time interval) The PRBs estimate of each operator can be calculated iteratively as follows: Est(n) is the average PRBs estimate count after n number of TTIs* PRBs_TTI(n) is the instantaneous PRBs count needed by the operator by the nth TTI n is the number of TTIs in the hypervisor allocation time interval (granularity) *TTI: transmission time interval (in LTE it is 1 ms) April 23,

13 Hypervisor Scheduler The hypervisor allocates the PRBs on the different virtual operators as follows: 1. Firstly, allocate PRBs to operators with the fixed guaranteed contract 2. Secondly, allocate PRBs to operators with the dynamic guaranteed contract based on the estimate number of PRBs (Est(n)), this should be upper bounded by the max value defined in their contract 3. Then, allocate PRBs to operators with the BE with minimum guarantees contract based only on the minimum value defined in their contract, this is to guarantee the minimum value 4. Finally, whatever left number of PRBs would be allocated to the BE operators with BE with minimum guarantees and BE with no guarantees contracts The allocation of the left PRBs to the BE operators in step 4 will be done based on a Fair Factor (FF) which is defined as follows: April 23,

14 Simulation Model and Results April 23, WARD Consortium

15 OPNET Simulation Model Hypervisor Physical enb Virtual enbs April 23,

16 Simulation Configuration The simulation is configured with 4 virtual operators each with one of the different contract types defined earlier: 1. Video streaming operator: with a fixed guaranteed contract of 33 PRBs 2. VOIP operator: configured with a dynamic guaranteed contract, with a max value of 33 PRBs 3. VOIP + BE Video on demand operator: configured with the best effort with min. guarantees contract, with min. and max. value of 25 and 45 consecutively 4. Small VOIP operator: configured with BE and no guarantees contract Two scenarios are configured one without virtualization legacy and one with virtualization virtualized. The traffic modes used are configured as follows: Table 2 April 23,

17 Virtual Operator (VO) allocated number of PRBs The figure shows the number of PRBs that each virtual operator has been allocated over time It can be noticed that for the first operator the PRBs allocation is fixed to 33 PRBs since it is using the fixed guaranteed contract For the other three operators we can notice that the allocated number of PRBs changes with time depending on the traffic load and the contract details of each operator April 23,

18 Virtual operator 1 (12 video users) Air interface throughput and app. end-to-end delay What can be noticed is that the operator has the same performance with and without virtualization; this is because this operator has a contract with a guaranteed fixed allocation April 23,

19 Virtual operator 2 (40 VOIP users) Air interface throughput What can be noticed is that the operator has the same performance with and without virtualization April 23,

20 Virtual operator 2 (40 VOIP users) Application end-to-end delay The application end-to-end delay of the operator has the same performance with and without virtualization April 23,

21 Virtual operator 2 Downlink used number of PRBs vs. time The previous results showed that operator 2 has the same performance with and without virtualization But, in the virtualized scenario operator 2 is not wasting the air interface resources since it only uses the required number of PRBs to serve the users as can be seen in the figure This is a big advantage since the operator will be able to cut cost because he will only pay for the resources used April 23,

22 Virtual operator 3 (16 VOIP+16 video users) Air interface throughput It can be noticed that users 1 16 (which are the VOIP users) have the same performance in both scenarios, whereas users (Video users) are having a slightly better performance in the virtualized scenario. April 23,

23 Virtual operator 3 Application end-to-end delay For the VOIP users (left side figure) we can see that similar performance is achieved in both scenarios. As for the video users (right side figure) one can notice that users are suffering from huge delay values for the legacy scenario due to buffering; whereas in the virtualized scenario the users are having good performance. The reason why the VOIP users in the legacy scenario are not affected is the fact that these users are being served with higher priority and the resources are enough to serve those users, but not enough to serve the video users. April 23,

24 Virtual operator 4 (3 VOIP users) Air interface throughput and app. end-to-end delay One additional advantage that can be achieved in the virtualized scenario is the ability to serve small operators with relatively smaller number of users in a pure best effort manner with whatever resources are left rather than wasting these resources April 23,

25 Conclusion The results demonstrate the additional advantages that can be achieved from applying network virtualization into the wireless world (in addition to being able to share the infrastructure and being able to change resources dynamically) Both operator 2 and 3 benefited from virtualization where: Operator 2 is able to cut costs by being able to use and pay only with respect to what he needs while still being able to guarantee his users performance Operator 3 is able to serve his users with better performance gaining from the use of the left resources The results also show the possibility of opening the market to new players (mainly small operators) that can serve very specific rule and have in general small number of users These operators can operate with the left number of resources that are normally not used and wasted in today s network April 23,

26 Outlook This work is a starting point of the LTE virtualization, as there are more issues to be investigated: Interference coordination among multiple virtual operators Signaling overhead due to the hypervisor in charge of the resource allocation Defining guidelines and scheduling disciplines for the hypervisor based on more enhanced criteria/contracts More diverse simulation scenarios.. Nevertheless, with LTE wireless virtualization operators can expect not only lower investment for flexible network deployment but also lower costs for network management and maintenance, meanwhile the enduser can expect better services with lower prices in the future. April 23,

27 Questions April 23,

28 BACKUP April 23,

29 LTE Downlink Physical Resources Structure Resource element QPSK 2bits 16QAM 4bits 64QAM 6bits 7 OFDM symbols 0.5 ms Time (sec) Inter-carrier subspacing 15 khz 1 Physical resource block (PRB) Frequency (Hz) 12 Subcarriers 12*15k=180kHz Sub-carrier April 23,