# A Baseband Wireless Spectrum Hypervisor for Multiplexing Concurrent OFDM Signals
## 5 Related Work
It emulates Additive White Gaussian Noise (AWGN), Rayleigh and Multi-path channels with several different Signal-to-Noise (SNR) values. The prototype makes extensive use of Single Instruction Multiple Data (SIMD) functions, including the FFT and IFFT implementations [48], making it even more optimized. Table 1 presents a comprehensive comparison of related virtualization and hypervision works. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Comparison Metric**} & \multicolumn{1}{c}{This work} & [23] & [43] & [44] & [41] & [45] & [27] & [46] & [47] & [21] & [42] \\ \hline Multiplexing domain & Frequency & Frequency & Frequency & Frequency & Time & Frequency & Frequency & Frequency & Frequency & Frequency & Time \\ \hline Virtual resource type & Spectrum & Spectrum & Spectrum & RB & AP in time & RB & Spectrum & RB & RB & Spectrum & AP in time \\ RAT agnostic & Only MC [10] & Yes & Yes & Only WiMax & Only Wi-Fi & Only LTE & Yes & Only WiMax/LTE & Only LTE & Yes & Only Wi-Fi \\ \hline Spectrum flexibility [11] & Yes & Yes & Yes & Yes & FC/FB [12] & Yes & Yes & Yes & Yes & Yes & FC/FB [12] \\ \hline Operation mode & S/FB & S & S & S & PB & S & S & S & S & S & P8 \\ \hline Simulation validated & Yes & No & No & Yes & No & No & No & No & Yes & No \\ \hline Experimentally validated & Yes & Yes & Yes & Yes & Yes & Yes & Yes & No & No & Yes & Yes \\ Implementation & SW & SW & SW & SW & SW & SW & SW & SW & SW & SW \\ Create self-interference & No [1] & Yes & Yes & No [1] & No [2] & No & Yes & No & No & Yes & No \\ Create COB emissions & Yes & Yes & Yes & No & Yes & No & Yes & No & Yes & Yes \\ Individual gain control & Yes & Yes & Yes & NA & No & No & No & Yes & NA & No & No \\ Open-source prototype & Yes & Yes & Yes & Yes & No & No & No & No & No & No & Yes & No \\ \hline Dynamic allocation [3] & Yes & No & Yes & NA & Yes & Yes & No & Yes & Yes & No & Yes \\ \hline Radio resource isolation [4] & Yes & Yes & Yes & Yes & Yes & Yes & Yes & Yes & Yes & Yes & Yes \\ \hline Virtual radio independence [5] & Yes & No & Yes & NA & Yes & Yes & Yes & Yes & Yes & Yes & Yes \\ Concurrent T/Vs at different channels & Yes & Yes & Yes & Yes & No [4] & Yes & No [4] & Yes & No [4] & Yes & No \\ \hline Number of VR instances [7] & 12 & 2 & 2 & 2.2 kilos [9] & 2.8 [FOOTNOTE:8]Footnote 8: **Legend**: RB: resource-block-MC; multi-carrier-AP; access-point-SW; software-S; streaming-PB; packet-based-NA; information not-available-VR; virtual radio-FC; fixed channel center frequency-PB; fixed channel bandwidth; \(1\) OFDM-based systems do not create self-interference as the subcarriers are mutually orthogonal. \(2\) One or time-multiplexing the access-point. \(3\) Allow on demand destruction and creation of VVs without interruping the operation of the spectrum hypervisor or other V/R. \(4\) Allocate non-overlapping sub-bands to different V/Rs and prevent interference among V/Rs, e.g., guard bands. \(5\) Ensure that V/S cannot interfere with the operation and performance of other V/S, even in the case of a malfunctioning or misbehaving V/Rs. \({}^{*}\) Use the concept of virtual RBs, therefore, concurrent transmissions only happen at different RBs with the same channel. \({}^{*}\) The maximum number of V/Rs instantiated during the experiments. \({}^{*}\) Assign a PPIV that is time-shared between two V/Rs. \({}^{*}\) Single PHY layer that has its RBs split into slices, creating V/Rs. \({}^{*}\) Optimized for multi-carrier-based waveforms, e.g., OFDM. \({}^{*}\) Flexibility in setting different channel center frequencies and bandwidths to different concurrent V/Rs. \({}^{12}\) The approach only works with fixed channel center frequencies and bandwidths as it time-multiplexes a Wi-Fi AP. & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of related works.