Pharmaceuticals and personal care products are recognized as emerging pollutants in water resources. Various treatment options have been investigated for the removal of pharmaceuticals that include both conventional (e.g., biodegradation, adsorption, activated sludge) and advanced (e.g., membrane, microfiltration, ozonation) processes. This article reviews literature for adsorptive removal of pharmaceuticals from water sources. Adsorbents from various origins were reviewed for their capacity to remove pharmaceuticals from water. These adsorbents include carbonaceous materials, clay minerals, siliceous adsorbents, and polymeric materials. The adsorption capacity of adsorbents to adsorb pharmaceuticals from water is discussed in this study. The review discusses the mechanism for adsorption of pharmaceuticals onto adsorbents as well. Finally, effectiveness of processing parameters during adsorption processes is presented

Akhtar, J.

Amin, N. A. S.

Shahzad, K.

Universiti Teknologi Malaysia Institutional Repository

Physical Layer Security in Two-Path SuccessiveRelayingQian Yu Liau and Chee Yen LeowWireless Communication Centre, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia.Email: qianyuliau@gmail.com, bruceleow@fke.utm.myAbstract—This paper proposes a bandwidth-efﬁcient transmis-sion protocol with one source, one destination and two assistinghalf-duplex relays. The two relays operate alternately in a time-division-duplex mode to forward messages from source to desti-nation in the presence of an eavesdropper. Therefore, the sourcetransmits new information continuously and the bandwidthefﬁciency of ideal full-duplex relay network can be achieved. Thetwo relays provide higher diversity gain compared to the existingschemes assisted by one relay. By considering the achievablesecrecy rate as the minimum between the secrecy rate of the S-Rand R-D links, the achievable secrecy capacity can be improved.We investigate the performance of the protocol in terms of ergodicsecrecy capacity and secrecy outage probability and compared tothe existing half-duplex relaying, full-duplex relaying and full-duplex jamming schemes. The proposed protocol achieves thehighest ergodic secrecy capacity and the lowest probability ofsecrecy outage compared to the existing schemes.Index Terms—Physical layer secrecy, cooperative relay net-works, two-path successive relaying, secrecy capacity, secrecyoutage probability.I. INTRODUCTIONThe ﬁfth generation (5G) network will serve as a key enablerin meeting the continuously increasing demands for futurewireless applications, including an ultra-high data rate, anultra-wide radio coverage, an ultra-large number of devices,and an ultra-low latency [1]. Owing to the broadcast nature ofwireless channels, the security of 5G wireless network fromeavesdropping remains one of the core challenges. Tradition-ally, information security has been addressed in the upperlayers based on cryptographic methods. Recently, physicallayer security is identiﬁed as a promising strategy that providessecure wireless transmissions by exploring the characteristicsof the wireless channel.The cooperative relaying approach has great potential toprovide substantial beneﬁts not only in terms of reliability (di-versity gain) and rate (bandwidth or spectral efﬁciency), alsohas the capability to enhance wireless security [2]–[4]. A con-ventional half-duplex relay cannot transmit and receive signalsimultaneously in the same frequency channel. Therefore, thesource has to keep silent and stop transmission of new messageduring the relay transmission phase. As a result, the spectralefﬁciency for conventional half-duplex relay is only half ofthe spectral efﬁciency of direct transmission. A full-duplexrelay can receive and transmit signals at the same time in thesame channel is proposed to improve the spectral efﬁciency ofcooperative relaying transmission. However, the reception ofthe full-duplex relay is interfered with its own transmission,which is called self-interference. The self-interference can beminimised by sophisticated hardware and/or advanced signalprocessing which signiﬁcantly increases the cost and com-plexity of relay nodes [5]–[7]. Compared to full-duplex relay,the implementation of a half-duplex relay is much easier andcheaper. Two-path successive relaying is proposed to achievethe full-duplex spectral efﬁciency by scheduling a pair of half-duplex relays to assist the source transmission alternately [8].Existing literature mainly considers the TPSR in conventionalscenarios without eavesdroppers [9]–[13]. The performance ofTPSR in secrecy communication remains open.In this paper, we propose a secrecy two-path successiverelaying protocol. We evaluate the performance of the two-path successive relaying network in terms of secrecy capacityand secrecy outage probability and compared to half-duplex re-laying, full-duplex relaying and full-duplex jamming schemesin [14].II. SYSTEM MODEL AND TRANSMISSION PROTOCOLA. System ModelConsider a wireless network consisting of one source (S),one destination (D), and two half-duplex relays (R1 and R2)in the presence of an eavesdropper (E) as shown in Figure1, where all nodes are equipped with a single antenna. Theeavesdropper can intercept the transmission from source andone relay during each time-slot, simultaneously. The R1 andR2 apply the decode-and-forward protocol. We assume thatdirect S-to-D link is not available, so transmission from S toD requires the assisting of R1 and R2.We assume that all channels experience block Rayleighfading and that the channels remain constant over one blockbut vary independently from one block to another. The channelcoefﬁcient from node i to node j is denoted as hij andreciprocal (hij = hji). The noise at relays (R1 and R2), Dand E are denoted as nr(t), nd(t) and ne(t) with variances ofσ2r , σ2d and σ2e respectively. The transmit power, P of sourceand relays are subject to unit power constraint.2015 IEEE 20th International Workshop on Computer Aided Modelling and Design of Communication Links and Networks(CAMAD)978-1-4673-8186-4/15/$31.00 ©2015 IEEE 180ℎℎℎ~~ℎℎS R1R2DEOdd time-slot, toS R1R2DEEven time-slot, teℎ ℎ~~ℎℎℎDesired Signal InterferenceFigure 1: The secrecy two-path successive relaying (TPSR)network with an eavesdropper.B. Transmission ProtocolThe transmission protocol of two-path successive relaying(TPSR) is divided into T + 1 consecutive equal-durationtime-slots and S transmits independent codeword xs(t), t =1, 2, . . . , T continuously. The protocol is alternated by oddtime-slot stage and even time-slot stage.• In odd time-slot (to = 1, 3, . . . , T + 1), S transmitsxs(to) and R2 forwards xs(to − 1). R1 receives xs(to)from S while being interfered with by R2 and D receivesxs(to−1) from R2. E receives xs(to) from S while beinginterfered with by R2.• In even time-slot (te = 2, 4, . . . , T ), S transmits xs(te)and R1 forwards xs(te − 1). R2 receives xs(te) fromS while being interfered with by R1 and D receivesxs(te−1) from R1. E receives xs(te) from S while beinginterfered with by R1.In the ﬁrst time-slot (t = 1) and the last time slot (t = T +1),R2 and S transmit artiﬁcial noise respectively to deterioratethe receiving signal of E from S. The protocol using T + 1time-slots to deliver T codewords from S to D, resulting ina bandwidth utilization efﬁciency equal to T/(T + 1), whichapproaches to one as T → ∞.The received signal at R1, D and E in to are respectivelygiven byyr1(to) =√P hsr1xs(to) +√P hrrxs(to − 1) + nr(to), (1)yd(to) =√P hr2d xs(to − 1) + nd(to), (2)ye(to) =√P hse xs(to) +√P hr2e xs(to − 1) + ne(to). (3)The received signal at R2, D and E in te are similar to(1), (2) and (3) respectively by simply exchanging subscriptR1 and R2. The the inter-relay interference can be mitigatedeffectively by spacing the two distributed relays sufﬁcientlyapart.III. SECRECY CAPACITYIn [14], the secrecy capacity is deﬁned as (see [15]),Cs = [Ct − Ce]+, (4)where [x]+ = max(x, 0), Ct and Ce are the capacities fordata transmission and eavesdropping respectively. Since, therelay apply decode-and-forward relaying, the capacity for datatransmission is given byCt = min (Csr, Crd) , (5)where Csr and Crd are the capacities for S-to-R and R-to-Dchannels. For the eavesdropping capacity, Ce, the eavesdroppercan decode the data from either S or R. Secrecy capacity canbe deﬁned asCs = min (Ssr, Srd) , (6)where Ssr and Srd are the secrecy rates for S-to-R and R-to-Dchannels.A. Independent Secrecy Transmission RateThe secrecy rates for S-to-R1 and R1-to-D channels aregiven bySsr1 =T2(T + 1)[log2(1 +P |hsr1 |2P |hrr|2 + σ2r)− log2(1 +P |hse|2P |hr2e|2 + σ2e)]+, (7)Sr1d =T2(T + 1)[log2(1 +P |hr1d|2σ2d)− log2(1 +P |hr1e|2P |hse|2 + σ2e)]+, (8)respectively, where T2(T+1) is the pre-log secrecy capacity ofR1. Then, secrecy capacity of R1 is given asCR1 = min (Ssr1 , Sr1d) . (9)Similarly, secrecy capacity of R2 can be deﬁned by simply ex-changing subscript R1 and R2 in (7), (8) and (9) respectively.Finally, the secrecy capacity for two-path successive relaying(TPSR) is the sum of CR1 and CR2 as followsCTPSR= CR1 + CR2 . (10)B. Secrecy Outage ProbabilityFrom (10), the secrecy outage probability for the TPSR isgiven byPTPSR= P (CTPSR< rs)= P (CR1 + CR2 < rs) , (11)where rs is the target secrecy rate.2015 IEEE 20th International Workshop on Computer Aided Modelling and Design of Communication Links and Networks(CAMAD)1810 5 10 15 20 25 30 35 40012345678910SNR (γsr = γrd) in dBErgodic Secrecy Capacity in bits/s/HzTPSR, γse = γre = 10dBFDJ, γse = γre = 10dBFDR, γse = γre = 10dBHDR, γse = γre = 10dBFigure 2: Ergodic secrecy capacity versus SNR where γsr =γrd, γse = γre = 10dB and the inter-relay interference andself-interference, γrr = 0dB.IV. NUMERICAL RESULTSIn this section, several Monte Carlo simulation resultsare provided to investigate the secrecy performance of theproposed two-path successive relaying (TPSR). The secrecyperformance of TPSR is compared to the half-duplex relaying(HDR), full-duplex relaying (FDR) and full-duplex jamming(FDJ) schemes. In the FDR, the full-duplex relay can receivexs(t) from S and forward the previously decoded xs(t − 1)to D simultaneously at time slot t. But, when the relay isreceiving xs(t) from S, it is interfered by its own transmissionwhich is called self-interference. In the FDJ, the full-duplexrelay and S transmits jamming signal to E at time slot t andtime slot t + 1 respectively to deteriorate the eavesdroppingcapacity. This decreases the spectral efﬁciency of FDJ to 1/2.The details of the comparison schemes are presented in [14].In the following simulations, the noise variances of all nodesand the transmit power of source and relay, P are normalizedto unity. There are T = 1000 independent codewords have tobe transmitted by S.Figure 2 and Figure 3 show the ergodic secrecy capacityversus SNR of various schemes when γsr = γrd, inter-relayinterference and residual self-interference, γrr = P/σ2r =0dB and γse = γre = 10dB (weak eavesdropping channels)and γse = γre = 30dB (strong eavesdropping channels)respectively. Regardless of weak or strong eavesdroppingchannels, the FDR and FDJ achieve higher ergodic secrecycapacity than the HDR. This is because the FDR has ahigher spectral efﬁciency compared to HDR, whereas theFDJ employs jamming technique to interfere the eavesdropper.When the eavesdropping channels are strong, the jammingtechnique beneﬁts the FDJ, whereas the secrecy capacity ofthe FDR is decreased by the increased eavesdropping capacity.On the other hand, the proposed TPSR shows its robustnessby achieving the similar ergodic secrecy capacity in both casesand outperforms the other schemes signiﬁcantly. The higher0 5 10 15 20 25 30 35 40012345678910SNR (γsr = γrd) in dBErgodic Secrecy Capacity in bits/s/Hz TPSR, γse = γre = 30dBFDJ, γse = γre = 30dBFDR, γse = γre = 30dBHDR, γse = γre = 30dBFigure 3: Ergodic secrecy capacity versus SNR where γsr =γrd, γse = γre = 30dB and the inter-relay interference andself-interference, γrr = 0dB.0 5 10 15 20 25 30 35 4010−510−410−310−210−1100SNR (γsr = γrd) in dBSecrecy Outage ProbabilityTPSR, r = 1, γse = γre = 10dBFDJ, rs = 1, γse = γre = 10dBFDR, rs = 1, γse = γre = 10dBHDR, rs = 1, γse = γre = 10dBFigure 4: Secrecy outage probability versus SNR where γsr =γrd, γse = γre = 10dB, rs = 1 bits/s/Hz and the inter-relayinterference and self-interference, γrr = 0dB.secrecy capacity of TPSR compared to the other schemes iscontributed by the deﬁnition of the secrecy rate in (6) and theuse of two relays.Figure 4 and Figure 5 show the secrecy outage probabilityversus SNR of various schemes when γsr = γrd, γrr = 0dB,target secrecy rate, rs = 1bits/s/Hz and γse = γre = 10dBand γse = γre = 30dB respectively. Same as the formersimulation, the HDR has the worst performance comparedto the other schemes in both cases by achieving the highestprobability of secrecy outage. Based on Figure 4 and Figure 5,the HDR and FDR only able to deliver the target secrecy ratewhen the channel gain of the main channels is greater than theeavesdropping channels. On the other hand, the FDJ and TPSRare able deliver the target secrecy rate even the channel gainof the main channels is less than the eavesdropping channels.2015 IEEE 20th International Workshop on Computer Aided Modelling and Design of Communication Links and Networks(CAMAD)1820 5 10 15 20 25 30 35 4010−410−310−210−1100SNR (γsr = γrd) in dBSecrecy Outage ProbabilityTPSR, rs = 1, γse = γre = 30dBFDJ, rs = 1, γse = γre = 30dBFDR, rs = 1, γse = γre = 30dBHDR, rs = 1, γse = γre = 30dBFigure 5: Secrecy outage probability versus SNR where γsr =γrd, γse = γre = 30dB, rs = 1 bits/s/Hz and the inter-relayinterference and self-interference, γrr = 0dB.This shows the robustness of the FDJ and TPSR. In the FDJ,the eavesdropping capacity is decreased signiﬁcantly whenthe eavesdropper has strong eavesdropping channels. This isbecause the eavesdropper is interfered by strong jammingsignals when it has strong eavesdropping channels. For theTPSR, there are several factors that support the TPSR toachieve the lowest probability of secrecy outage compared tothe other schemes in both cases. The ﬁrst factor is the higherspectral efﬁciency of TPSR compared to the HDR and FDJ.The second factor is the higher diversity gain compared to theother schemes that provided by the two distributed half-duplexrelays in TPSR.V. CONCLUSIONIn this paper, TPSR is proposed to improve the security forthe transmission of the source and relays from interception.The numerical results reveal that the proposed TPSR has bettersecrecy performance compared to the other schemes in termsof ergodic secrecy capacity and secrecy outage probability.This is because the proposed TPSR achieves higher spectralefﬁciency compared to the HDR and FDJ. In additional,the two half-duplex relays provide higher diversity gain forthe TPSR compared to the FDR. In short, with the TPSRprotocol, the secured wireless transmission can be achievedby using conventional half-duplex relays without employingsophisticated jamming techniques.ACKNOWLEDGMENTThis research is supported by the Ministry of Science, Tech-nology and Innovation Malaysia (MOSTI), the Ministry of Ed-ucation Malaysia (MOE) and University Teknologi Malaysiaunder Project Vote No. 4S079, 4F261 and 05H39.REFERENCES[1] N. Yang, L. Wang, G. Geraci, M. Elkashlan, J. Yuan, and M. Di Renzo,“Safeguarding 5g wireless communication networks using physical layersecurity,” Communications Magazine, IEEE, vol. 53, no. 4, pp. 20–27,April 2015.[2] P. Popovski and O. Simeone, “Wireless secrecy in cellular systems withinfrastructure-aided cooperation,” Information Forensics and Security,IEEE Transactions on, vol. 4, no. 2, pp. 242–256, June 2009.[3] Y. Zou, X. Wang, and W. Shen, “Physical-layer security with multiuserscheduling in cognitive radio networks,” CoRR, vol. abs/1311.0404,2013. [Online]. Available: http://arxiv.org/abs/1311.0404[4] Y. Zou, J. Zhu, X. Wang, and V. Leung, “Improving physical-layer se-curity in wireless communications using diversity techniques,” Network,IEEE, vol. 29, no. 1, pp. 42–48, Jan 2015.[5] D. Bliss, T. Hancock, and P. Schniter, “Hardware phenomenologicaleffects on cochannel full-duplex mimo relay performance,” in Signals,Systems and Computers (ASILOMAR), 2012 Conference Record of theForty Sixth Asilomar Conference on, Nov 2012, pp. 34–39.[6] T. Riihonen, S. Werner, and R. Wichman, “Mitigation of loopbackself-interference in full-duplex mimo relays,” Signal Processing, IEEETransactions on, vol. 59, no. 12, pp. 5983–5993, Dec 2011.[7] O. Taghizadeh and R. Mathar, “Full-duplex decode-and-forward relayingwith limited self-interference cancellation,” in Smart Antennas (WSA),2014 18th International ITG Workshop on, March 2014, pp. 1–7.[8] B. Rankov and A. 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El Gamal, “On the secrecy capacity offading channels,” Information Theory, IEEE Transactions on, vol. 54,no. 10, pp. 4687–4698, Oct 2008.2015 IEEE 20th International Workshop on Computer Aided Modelling and Design of Communication Links and Networks(CAMAD)183

A review on removal of pharmaceuticals from water by adsorption

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A review on removal of pharmaceuticals from water by adsorption

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