1 Introduction
2 Background and related works
3 Radio resource management in virtual RANs
3.1 Model
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Guaranteed bitrate (GB), in which the RAN provider guarantees the VNO a minimum and a maximum level of data rates, regardless of the network status. Allocating the maximum guaranteed data rate to the VNO leads to its full satisfaction. The upper boundary in this type of SLA enables VNOs to have full control on their networks. For instance, a VNO offering VoIP (voice over IP) to its subscribers may foresee to offer this service to only 30 up 50% of its subscribers simultaneously, hence, the VNO can put this policy into practice by choosing a guaranteed SLA for its VoIP service. It is expected that subscribers always experience a good quality of service (QoS) in return of relatively more expensive services.
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Best effort with minimum guaranteed (BG), where the VNO is guaranteed with a minimum level of service. The request for data rates higher than the guaranteed level is served in the best effort manner, hence, the minimum guaranteed data rate is the one received during busy hours. In this case, although VNOs do not invest as much as former ones, they can still guarantee the minimum QoS to their subscribers. From the subscribers’ viewpoint, the acceptable service (not as good as the previous ones) is offered with a relatively lower cost.
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Best effort (BE), in which the VNO is served in the pure best effort approach. In this case, operators and their subscribers may suffer from low QoS and resource starvation during busy hours, but the associated cost will be lower as well.
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\( {s}_{\mathrm{t}}^{\mathrm{RRU}} \): the set of radio resources at t,
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\( {N}_{\mathrm{SRRU}}^{\mathrm{RA}{\mathrm{T}}_{\mathrm{i}}} \): number of spare RRUs in the ith RAT,
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N RAT: number of RATs.
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\( {R}_{\mathrm{b}}^{\mathrm{CRRM}} \): total network data rate.
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\( {R}_{{\mathrm{b}}_{\mathrm{ji}}}^{\mathrm{Srv}} \): serving (allocated) data rate for service j of VNO i;
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N VNO: number of VNOs;
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N srv: number of services.
3.2 Estimation of available resources
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\( {R_{\mathrm{b}}}_{\mathrm{RA}{\mathrm{T}}_{\mathrm{i}}} \): data rate of an RRU from the ith RAT,
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ρ in:SINR,
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\( {R_{\mathrm{b}}}_{\mathrm{RA}{\mathrm{T}}_{\mathrm{i}}}^{\max } \):maximum data rate of an RRU from the ith RAT.
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\( {N}_{\mathrm{RRU}}^{\mathrm{RA}{\mathrm{T}}_{\mathrm{i}}} \): number of RRUs of the ith RAT,
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\( {R}_{{\mathrm{b}}_{\mathrm{tot}}}^{\mathrm{RA}{\mathrm{T}}_{\mathrm{i}}} \): data rate from the ith RAT pool,
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\( {R}_{{\mathrm{b}}_{\mathrm{n}}}^{\mathrm{RA}{\mathrm{T}}_{\mathrm{i}}} \): data rate from the nth RRU of the ith RAT.
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Optimistic approach (OP): all RRUs are assigned to users with very good channel quality (i.e., high SINR), therefore, it is assumed that the data rate of each RRU satisfies:
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Realistic approach (RL): it is assumed that the RRUs of each RAT are divided into two equal groups, and that the data rate of the RRU from each group is as follows:
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Pessimistic approach (PE): it is assumed that all the RRUs in the system are assigned to users with low SINR so that the boundaries are
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R bLow: low boundary for the RRU data rate;
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R bHigh: high boundary for the RRU data rate.
3.3 Allocation of resources in cellular networks
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\( {\mathbf{R}}_{\mathbf{b}}^{\mathbf{cell}} \): vector of serving data rates from cellular networks,
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N VNO: number of served VNOs by this VRRM,
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N srv: number of services for each VNO,
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\( {W}_{\mathrm{ji}}^{\mathrm{Srv}} \): weight of serving unit of data rate for service j of VNO i by VRRM, where \( {W}_{\mathrm{ji}}^{\mathrm{Srv}}\in \left[0,1\right] \).
3.4 Allocation of resources in WLAN
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\( {\mathbf{R}}_{\mathbf{b}}^{\mathbf{WLAN}} \): vector of serving data rates from APs,
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W SRb: weight for session average data rate, where W S Rb ? [0, 1],
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\( \overline{R_b^{max}} \): maximum average data rate among all services,
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\( \overline{R_{{\mathrm{b}}_{\mathrm{j}}}} \): average data rate for service j.
3.5 Fairness
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\( {R}_{{\mathrm{b}}_{\mathrm{ji}}}^{\mathrm{f}} \): the boundary for deviation data rate from the normalised average for service j of VNO i, defined as:
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\( {\mathbf{R}}_{\mathbf{b}}^{\mathbf{f}} \): vector of intermediate fairness variables,
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\( {\mathbf{R}}_{\mathbf{b}}^{\mathbf{Srv}} \): vector of serving data rates,
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α f : fairness coefficient as a function of fairness weight:
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N SmaxRb: number of subscribers using the service with maximum data rate,
3.6 Constraints
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\( {R}_{{\mathrm{b}}_{\mathrm{ji}}}^{\mathrm{Min}} \): minimum data rate for service j of VNO i,
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\( {R}_{{\mathrm{b}}_{\mathrm{ji}}}^{\mathrm{Max}} \): maximum data rate for service j of VNO i.
3.7 Resource allocation with violation
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\( \varDelta {R}_{{\mathrm{b}}_{\mathrm{ji}}}^{\mathrm{v}} \): non-negative violation variable for the minimum guaranteed data rate of service j of VNO i.
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\( \varDelta \overline{R_{\mathrm{b}}^{\mathrm{v}}} \): average constraint violation.
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\( {W}_{\mathrm{ji}}^{\mathrm{v}} \): weight of violating minimum guaranteed data rate of service j of VNO i¸ where \( {W}_{\mathrm{ji}}^{\mathrm{v}}\in \left[0,1\right] \) .
4 Scenario
RAT | Number of cells | Cell radius [km] | System |
\( {N}_{\mathrm{RRU}}^{\mathrm{RA}{\mathrm{T}}_{\mathrm{i}}} \)
|
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OFDM | 16.0 | 0.08 | Wi-Fi | 40 |
OFDMA | 16.0 | 0.4 | LTE | 8 000 |
CDMA | 1.7 | 1.2 | UMTS | 80 |
TDMA | 1.0 | 1.6 | GSM | 75 |
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The OFDMA cells, with a 400 m radius, are the smallest ones; based on the 100 MHz LTE-Advanced feature, each cell has 500 RRUs to be assigned to traffic bearers.
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The configurations of CDMA cells are chosen according to UMTS/HSPA+, at 2.1 GHz, each cell with a 1.2 km radius and 3 carriers (each carrier has 16 codes); only 45 codes, out of all 48 in each cell, are assigned to users’ traffic.
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The FDMA/TDMA cells are the biggest ones, with a 1.6 km radius, based on GSM900, each cell having 10 radio channels (each one has 8 timeslots), being assumed that 75 timeslots out of the total 80 available ones in each cell are used for users’ traffic.
Service | Volume [%] |
\( {W}_{\mathrm{ji}}^{\mathrm{Srv}} \)
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\( {W}_{\mathrm{ji}}^{\mathrm{v}} \)
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\( \overline{R_{\mathrm{b}\left[\mathrm{kbps}\right]}} \)
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Video calling (ViC) | 59.7 | 95.4 | 0.3 | 0.27 | 5120.0 | |
Video streaming (ViS) | 4.6 | 0.4 | 0.36 | 384.0 | ||
File sharing (FTP) | 3.5 | 0.2 | 0.18 | 1024.0 | ||
Web browsing (WWW) | 11.9 | 0.2 | 0.18 | 500.0 | ||
Social networking (SoN) | 14.4 | 0.2 | 0.18 | 384.0 | ||
M2M | Smart metres (MMM) | 5.5 | 25 | 0.01 | 0.09 | 200.0 |
e-Health (MME) | 25 | 0.2 | 0.18 | 200.0 | ||
Intelligent transport services (MMI) | 25 | 0.4 | 0.36 | 200.0 | ||
Surveillance (MMS) | 25 | 0.3 | 0.27 | 200.0 | ||
Email (Ema) | 1 | 0.01 | 0.09 | 100.0 | ||
Music streaming (MuS) | 3 | 0.03 | 0.27 | 64.0 | ||
VoIP (VoI) | 1 | 0.04 | 0.36 | 12.2 |
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VNO GB: the data rates allocated to services are guaranteed to be in the range of 50 to 100% of the corresponding service data rate.
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VNO BG: it has the best effort, with a minimum 25% of the service data rate guaranteed by the SLA.
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VNO BE: it has all services served in the best effort approach, without any guarantee.
5 Results
5.1 Network capacity
RAT | OFDMA | CDMA | TDMA | OFDM | |
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PE | Min. \( {R}_{b_{\mathrm{tot}}\left[\mathrm{Gbps}\right]}^{\mathrm{RAT}} \)
| 0 | 0 | 0 | 0 |
Max. \( {R}_{b_{\mathrm{tot}}\left[\mathrm{Gbps}\right]}^{\mathrm{RAT}} \)
| 2.73 | 1.68 | 0.002 | 25.35 | |
RL | Min. \( {R}_{b_{tot}\left[\mathrm{Gbps}\right]}^{\mathrm{RAT}} \)
| 1.37 | 0.84 | 0.001 | 12.67 |
Max. \( {R}_{b_{\mathrm{tot}}\left[\mathrm{Gbps}\right]}^{\mathrm{RAT}} \)
| 4.10 | 2.52 | 0.003 | 38.08 | |
OP | Min. \( {R}_{b_{\mathrm{tot}}\left[\mathrm{Gbps}\right]}^{\mathrm{RAT}} \)
| 2.73 | 1.68 | 0.002 | 25.35 |
Max. \( {R}_{b_{\mathrm{tot}}\left[\mathrm{Gbps}\right]}^{\mathrm{RAT}} \)
| 5.47 | 3.36 | 0.004 | 50.78 | |
G | Min. \( {R}_{b_{\mathrm{tot}}\left[\mathrm{Gbps}\right]}^{\mathrm{RAT}} \)
| 0 | 0 | 0 | 0 |
Max. \( {R}_{b_{\mathrm{tot}}\left[\mathrm{Gbps}\right]}^{\mathrm{RAT}} \)
| 5.47 | 3.36 | 0.004 | 50.78 |