4 posts tagged with "federated learning"

In previous part, we have discussed about Autonomous driving FADNetwork. In this post, we will verify the effectiveness and efficiency of it.

Our source code can be found at: https://github.com/aioz-ai/FADNet

#1. Experimental Setup

Udacity. We use the popular Udacity dataset to evaluate our results. We only use front-forwarded images in this dataset in our experiment. We use $5$ sequences for training and $1$ for testing. The training sequences are assigned randomly to different silos depending on the federated topology (i.e., Gaia or NWS).

Carla. Since the Udacity dataset is collected in the real-world environment, changing the weather or lighting conditions is not easy. To this end, we collect more simulated data in the Carla simulator. We have applied different lighting (morning, noon, night, sunrise, sunset) and weather conditions (cloudy, rain, heavy rain, wet streets, windy, snowy) when collecting the data. We have generated $73,235$ samples distributed over $11$ sequences of scenes.

Gazebo. Since both the Udacity and Carla datasets are collected in outdoor environments, we also employ Gazebo to collect data for autonomous navigation in indoor scenes. We use a simulated mobile robot and the built-in scenes to collect data. Table.1 shows the statistics of three datasets. We use $80\%$ of the collected data in Gazebo and Carla data for training, and the rest $20\%$ for testing.

Network Topology. We conduct experiments on two topologies: the Internet Topology Zoo (Gaia), and the North America data centers (NWS). We use Gaia topology in our main experiment and provide the comparison of two topologies in our ablation study.

Training. The model in a silo is trained with a batch size of $32$ and a learning rate of $0.001$ using Adam optimizer. We follow the training process to obtain a global weight of all silos. The training process is conducted with $3000$ communication rounds and each silo has one NVIDIA 1080 11 GB GPU for training. Note that, one communication round is counted each time all silos have finished updating their model weights.

Baselines. We compare our results with various recent methods, including Random baseline and Constant baseline, Inception-V3, MobileNet-V2, VGG-16, and Dronet. All these methods use the Centralized Local Learning (CLL) strategy (i.e., the data are collected and trained in one local machine.) For distributed learning, we compare our Deep Federated Learning (DFL) approach with the Server-based Federated Learning (SFL) strategy. As the standard practice, we use the root-mean-square error (RMSE) metric to evaluate the results.

#2. Results

Table 2 summarises the performance of our method and recent state-of-the-art approaches. We notice that our FADNet is trained using the proposed peer-to-peer DFL using the Gaia topology with 11 silos. This table clearly shows our FDANet + DFL outperforms other methods by a fair margin. In particular, our FDANet + DFL significantly reduces the RMSE in Gazebo and Carla datasets, while slightly outperforms DroNet in the Udacity dataset. These results validate the robustness of our FADNet while is being trained in a fully decentralized setting. Table 3 also shows that with a proper deep architecture such as our FADNet, we can achieve state-of-the-art accuracy when training the deep model in FL. Fig. 2 illustrates the spatial support regions when our FADNet making the prediction. Particularly, we can see that FADNet focuses on the ``line-like" patterns in the input frame, which guides the driving direction.

#3. Ablation Studies

#Effectiveness of our DFL.

Table 3 summarises the accuracy of DroNet and our FADNet when we train them using different learning methods: CLL, SFL, and our peer-to-peer DFL. From this table, we can see that training both DroNet and FADNet with our peer-to-peer DFL clearly improves the accuracy compared with the SFL approach. This confirms the robustness of our fully decentralized approach and removes a need of a central server when we train a deep network with FL. Compared with the traditional CLL approach, our DFL also shows a competitive performance. However, we note that training a deep architecture using CLL is less complicated than with SFL or DFL. Furthermore, CLL is not a federated learning approach and does not take into account the privacy of the user data.

#Effectiveness of our FADNet.

Table 3 shows that apart from the learning method, the deep architectures also affect the final results. This table illustrates that our FADNet combined with DFL outperforms DroNet in all configurations. We notice that DroNet achieves competitive results when being trained with CLL. However DroNet is not designed for federated training, hence it does not achieve good accuracy when being trained with SFL or DFL. On the other hand, our introduced FADNet is particularly designed with dedicated layers to handle the data imbalance and model convergence problem in federated training. Therefore, FADNet achieves new state-of-the-art results in all three datasets.

#Network Topology Analysis.

Table 4 illustrates the performance of DroNet and our FADNet when we train them using DFL under two distributed network topologies: Gaia and NWS. This table shows that the results of DroNet and FADNet under DFL are stable in both Gaia and NWS distributed networks. We note that the NWS topology has 22-silos while the Gaia topology has only 11 silos. This result validates that our FADNet and DFL do not depend on the distributed network topology. Therefore, we can potentially use them in practice with more silo data.

#Convergence Analysis.

The effectiveness of federated learning algorithms is identified through the convergence ability, including accuracy and training speed, especially when dealing with the increasing number of silos in practice. Fig.3 shows the convergence ability of our FADNet with DFL using two topologies: Gaia with 11 silos, and NWS with 22 silos. This figure shows that our proposed DFL achieves the best results in Gaia and NWS topology and converges faster than the SFL approach in both Gazebo and Carla datasets. We also notice that the performance of our DFL is stable when there is an increase in the number of silos. Specifically, training our FADNet with DFL reaches the converged point after approximately $150$s, $180$s on the NWS and Gaia topology, respectively. Fig.3 validates the convergence ability of our FADNet and DFL, especially when dealing with the increasing number of silos.

In practice, compared with the traditional CLL approach, federated learning methods such as SFL or DFL can leverage more GPUs remotely. Therefore, we can reduce the total training time significantly. However, the drawback of federated learning is we would need more GPUs in total (ideally one for each silo), and deep architecture also should be carefully designed to ensure model convergence.

#Deployment

To verify the effectiveness of our FADNet in practice, we deploy the model trained on the Gazebo dataset on a mobile robot. The robot is equipped with a RealSense camera to capture the front RGB images. Our FADNet is deployed on a Qualcomm RB5 board to make the prediction of the steering angle for the robot. The processing time of our FADNet on the Qualcomm RB5 board is approximately $12$ frames per second. Overall, we observe that the robot can navigate smoothly in an indoor environment without colliding with obstacles. More qualitative results can be found in our supplementary material.

#Conclusion

We propose a new approach to learn an autonomous driving policy from sensory data without violating the user's privacy. We introduce a peer-to-peer deep federated learning (DFL) method that effectively utilizes the user data in a fully distributed manner. Furthermore, we develop a new deep architecture - FADNet that is well suitable for distributed training. The intensive experimental results on three datasets show that our FADNet with DFL outperforms recent state-of-the-art methods by a fair margin. Currently, our deployment experiment is limited to a mobile robot in an indoor environment. In the future, we would like to test our approach with more silos and deploy the trained model using an autonomous car on man-made roads.

Autonomous driving is an active research topic in both academia and industry. However, most of the existing solutions focus on improving the accuracy by training learnable models with centralized large-scale data. Therefore, these methods do not take into account the user's privacy. In this paper, we present a new approach to learn autonomous driving policy while respecting privacy concerns. We propose a peer-to-peer Deep Federated Learning (DFL) approach to train deep architectures in a fully decentralized manner and remove the need for central orchestration. We design a new Federated Autonomous Driving network (FADNet) that can improve the model stability, ensure convergence, and handle imbalanced data distribution problems while is being trained with federated learning methods. Intensively experimental results on three datasets show that our approach with FADNet and DFL achieves superior accuracy compared with other recent methods. Furthermore, our approach can maintain privacy by not collecting user data to a central server.

Our source code can be found at: https://github.com/aioz-ai/FADNet

#1. Introduction

In this paper, our goal is to develop an end-to-end driving policy from sensory data while maintaining the user's privacy by utilizing FL. We address the key challenges in FL to make sure our deep network can achieve competitive performance when being trained in a fully decentralized manner. Fig.1 shows an overview of different learning approaches for autonomous driving. In Centralized Local Learning (CLL), the data are collected and trained in one local machine. Hence, the CLL approach does not take into account the user's privacy. The Server-based Federated Learning (SFL) strategy requires a central server to orchestrate the training process and receive the contributions of all clients. The main limitation of SFL is communication congestion when the number of clients is large. Therefore, we follow the peer-to-peer federated learningto set up the training. Our peer-to-peer Deep Federated Learning (DFL) is fully decentralized and can reduce communication congestion during training. We also propose a new Federated Autonomous Driving network (FADNet) to address the problem of model convergence and imbalanced data distribution. By training our FADNet using DFL, our approach outperforms recent state-of-the-art methods by a fair margin while maintaining user data privacy.

Our contributions can be summarized as follows:

• We propose a fully decentralized, peer-to-peer Deep Federated Learning framework for training autonomous driving solutions.
• We introduce a Federated Autonomous Driving network that is well suitable for federated training.
• We introduce two new datasets and conduct intensive experiments to validate our results.

#2. Problem Formulation

We consider a federated network with $N$ siloed data centers (e.g., autonomous cars) $\mathcal{D}_{i}$, with $i \in [1,N]$. Our goal is to collaboratively train a global driving policy $\theta$ by aggregating all local learnable weights $\theta_i$ of each silo. Note that, unlike the popular centralized local training setup, in FL training, each silo does not share its local data, but periodically transmits model updates to other silos.

In practice, each silo has the training loss $\mathcal{L}_i(\xi_i, \theta_i)$. $\xi_i$ is the ground-truth in each silo $i$. $\mathcal{L}_i(\xi_i, \theta_i)$ is calculated as the regression loss. This regression loss is modeled by a deep network that takes RGB images as inputs and predicts the associated steering angles.

#3. Deep Federated Learning for Autonomous Driving

A popular training method in FL is to set up a central server that orchestrates the training process and receives the contributions of all clients (Server-based Federated Learning - SFL). The limitation of SFL is the server potentially represents a single point of failure in the system. We also may have communication congestion between the server and clients when the number of clients is massive. Therefore, in this work, we utilize the peer-to-peer FL to set up the training scenario. In peer-to-peer FL, there is no centralized orchestration, and the communication is via peer-to-peer topology. However, the main challenge of peer-to-peer FL is to assure model convergence and maintain accuracy in a fully decentralized training setting.

Fig.2 illustrates our Deep Federated Learning (DFL) method. Our DFL follows the peer-to-peer FL setup with the goal to integrate a deep architecture into a fully decentralized setting that ensures convergence while achieving competitive results compared to the traditional Centralized Local Learning or SFL approach. In practice, we can consider a silo as an autonomous car. Each silo maintains a local learnable model and does not share its data with other silos. We represent the silos as vertices of a communication graph and the FL is performed on an overlay, which is a sub-graph of this communication graph.

#Designing the Overlay

Let $\mathcal{G}_c = (\mathcal{V}, \mathcal{E}_c)$ is the connectivity graph that captures the possible direct communications among $N$ silos. $\mathcal{V}$ is the set of vertices (silos), while $\mathcal{E}_c$ is the set of communication links between vertices. $\mathcal{N}_i^{+}$ and $\mathcal{N}_i^{-}$ are in-neighbors and out-neighbors of a silo $i$, respectively. As in~\cite{marfoq2020throughput}, we note that it is unnecessary to use all the connections of the connectivity graph for FL. Indeed, a sub-graph called an overlay, $\mathcal{G}_o = (\mathcal{V}, \mathcal{E}_o)$ can be generated from $\mathcal{G}_c$. In our work, $\mathcal{G}_o$ is the result of Christofides’ Algorithm~\cite{monnot2003approximation}, which yields a strong spanning sub-graph of $\mathcal{G}_c$ with minimal cycle time. One cycle time or time per communication round, in general, is the time that a vertex waits for messages from the other vertices to do a computational update.

In practice, one block cycle time of an overlay $\mathcal{G}_o$ depends on the delay of each link $(i, j)$, denoted as $d_o(i, j)$, which is the time interval between the beginning of a local computation at node $i$, and the receiving of $i$'s messages by $j$. Furthermore, without concerns about access links delays between vertices, our graph is treated as an edge-capacitated network with:

where $T_c(i)$ is the time to compute one local update of the model; $s$ is the number of local computational steps; $l(i,j)$ is the link latency; $M$ is the model size; $B(i,j)$ is available bandwidth of the path $(i,j)$. As in~\cite{marfoq2020throughput}, we set $s=1$.

#Training Algorithm

At each silo $i$, the optimization problem to be solved is:

We apply the distributed federated learning algorithm, DPASGD, to solve the optimizations of all the silos. In fact, after waiting one cycle time, each silo $i$ will receive parameters $\theta_j$ from its in-neighbor $\mathcal{N}_i^{+}$ and accumulate these parameters multiplied with a non-negative coefficient from the consensus matrix $\mathbf{A}$. It then performs $s$ mini-batch gradient updates before sending $\theta_i$ to its out-neighbors $\mathcal{N}_i^{-}$, and the algorithm keeps repeating. Formally, at each iteration $k$, the updates are described as:

where $m$ is the mini-batch size and $\alpha_k > 0$ is a potentially varying learning rate.

#Federated Averaging

To compute the prediction of models in all silos, we compute the average model $\theta$ using weight aggregation from all the local model $\theta_i$. The federated averaging process is conducted as follow:

where $N$ is the number of silos; $\lambda_i = \{0,1\}$. Note that $\lambda_i = 1$ indicates that silo $i$ joins the inference process and $\lambda_i = 0$ if not. The aggregated weight $\theta$ is then used for evaluation on the testing set $\mathcal{D}_{test}$.

#4. Network Architecture

One of the main challenges when training a deep network in FL is the imbalanced and non-IID (identically and independently distributed) problem in data partitioning across silos. To overcome this problem, the learning architecture should have an appropriate design to balance the trade-off between convergence ability and accuracy performance. In practice, the deep architecture has to deal with the high variance between silo weights when the accumulation process for all silos is conducted. To this end, we design a new Federated Autonomous Driving Network, which is based on ResNet8, as shown in Fig.3.

In particular, our proposed FADNet first comprises an input layer normalization to improve the stability of the abstract layer. This layer aims to handle different distributions of input images in each silo. Then, a convolution layer following by a max-pooling layer is added to encode the input. To handle the vanishing gradient problem, three residual blocks are appended with a following FC layer to extract ResBlock features. However, using residual blocks increases the variance of silo weights during the aggregation process and affects the convergence ability of the model. To address this problem, we add a Global Average Pooling layer (GAP) associated with each residual block. GAP is a non-weight pooling layer which sums out the spatial information from each residual block. Thus, it is not affected by the weighted variance problem. The output of each GAP layer is passed through an Accumulation layer to accrue the Support feature. The ResBlock feature and the Support feature from GAP layers are fed into the Aggregation layer to calculate the model loss in each silo.

In our design, the Accumulation and Aggregation layers aim to reduce the variance of the global model since we need to combine multiple model weights produced by different silos. In particular, the Accumulation layer is a variant of the fully connected (FC) layer. Instead of weighting the contribution of input nodes as in FC, the Accumulation layer weights the contribution of multiple features from input layers. The Accumulation layer has a learnable weight matrix $w \in \mathbb{R}^\text{n}$. Its number of nodes is equal to the \text{n} number of input layers. Note that the support feature from the Accumulation layer has the same size as the input. Let $F = \{f_\text{1}, f_\text{2}, ..., f_\text{n}\}, \forall f_\text{h} \in \mathbb{R}^\text{d}$ be the collection of $\text{n}$ number of the features extracted from $\text{n}$ input GAP layers; $\text{d}$ is the unified dimension. The Accumulation outputs a feature $f_\text{c} \in \mathbb{R}^\text{d}$ in each silo $i$, and is computed as:

The Aggregation layer is a fusion between the ResBlock feature extracted from the backbone and the support feature from the Accumulation layer. For simplicity, we use the Hadamard product to compute the aggregated feature. This feature is then averaged to predict the steering angle. Let $f_\text{s} \in \mathbb{R}^\text{d}$ be the ResBlock features extracted from the backbone. The output driving policy $\theta_i$ of silo $i$ can be calculated as:

where $\odot$ denotes Hadamard product; $\bar{(*)}$ denotes the mean and we set $\text{d} = 6,272$.

#Next

In the next post, we will show the effectiveness and efficiency of FADNet during Federated Learning proccess.

#Federated learning and its remaining challenge

Federated learning is the process of training statistical models via a network of distant devices or siloed data centers, such as mobile phones or hospitals, while keeping data locally. In terms of federated learning, there are five major obstacles that have a direct impact on the paper publishing trend.

#1. Expensive Communication

Due to the internet connection, huge number of users, and administrative costs, there is a bottleneck in communication between devices and server-devices.

#2. Systems Heterogeneity

Because of differences in hardware (CPU, RAM), network connection (3G, 4G, 5G, wifi), and power, each device in federated networks may have different storage, computational, and communication capabilities (battery level).

#3. Statistical Heterogeneity

Devices routinely create and collect data in non-identically dispersed ways across the network; for example, in the context of a next word prediction, mobile phone users employ a variety of languages. Furthermore, the quantity of data points on different devices may differ greatly, and an underlying structure may exist that describes the interaction between devices and their related distributions. This data generation paradigm violates frequently-used independent and identically distributed (I.I.D. problem) assumptions in distributed optimization, increases the likelihood of stragglers, and may add complexity in terms of modeling, analysis, and evaluation.

#4. Privacy Concerns

In federated learning applications, privacy is a crucial problem. Federated learning takes a step toward data protection by sharing model changes, such as gradient information, rather than the raw data created on each device. Nonetheless, transmitting model updates during the training process may divulge sensitive information to a third party or the central server.

#5. Domain transfer

Not any task can be applied to the federated learning paradigm to finish their training process due to the aforementioned four challenges.

#Hot trends

#Data distribution heterogeneity and label inadequacy.

• Distributed Optimization
• Non-IID and Model Personalization
• Semi-Supervised Learning
• Vertical Federated Learning
• Decentralized FL
• Hierarchical FL
• Neural Architecture Search
• Transfer Learning
• Continual Learning
• Domain Adaptation
• Reinforcement Learning
• Bayesian Learning

#Security, privacy, fairness, and incentive mechanisms:

• Adversarial-Attack-and-Defense
• Privacy
• Fairness
• Interpretability
• Incentive Mechanism

#Communication and computational resource constraints, software and hardware heterogeneity, the FL system

• Communication-Efficiency
• Straggler Problem
• Computation Efficiency
• Wireless Communication and Cloud Computing
• FL System Design

#Models and Applications

• Models
• Natural language Processing
• Computer Vision
• Health Care
• Transportation
• Recommendation System
• Speech
• Finance
• Smart City
• Robotics
• Networking
• Blockchain
• Other

#Benchmark, Dataset, and Survey

• Benchmark and Dataset
• Survey

Federated Learning: machine learning over a distributed dataset, where user devices (e.g., desktop, mobile phones, etc.) are utilized to collaboratively learn a shared prediction model while keeping all training data locally on the device. This approach decouples the ability to do machine learning from storing the data in the cloud.

Conceptually, federated learning proposes a mechanism to train a high-quality centralized model. Simultaneously, training data remains distributed over many clients, each with unreliable and relatively slow network connections.

The idea behind federated learning is as conceptually simple as its technologically complex. Traditional machine learning programs relied on a centralized model for training in which a group of servers runs a specific model against training and validation datasets. That centralized training approach can work very efficiently in many scenarios. Still, it has also proven to be challenging in use cases involving a large number of endpoints using and improving the model. The prototypical example of the limitation of the centralized training model can be found in mobile or internet of things(IoT) scenarios. The quality of a model depends on the information processed across hundreds of thousands or millions of devices. Each endpoint can contribute to a machine learning model's training in its own autonomous way in those scenarios. In other words, knowledge is federated.

Blockchain: large, distributed dataset, where no-one can edit/delete an old entry, nor fake a new entry. The data is enforced by fundamental limits of computations (i.e., Proof of Work).

Smart Contract: dataset stored on the Blockchain, which includes: Data (i.e., ledgers, events, statistics), State (today's ledger, today's events), Code (rules for changing state).

#Math Examples

Fundamental Theorem of Calculus Let $f:[a,b] \to \R$ be Riemann integrable. Let $F:[a,b]\to\R$ be $F(x)= \int_{a}^{x}f(t)dt$. Then $F$ is continuous, and at all $x$ such that $f$ is continuous at $x$, $F$ is differentiable at $x$ with $F'(x)=f(x)$.

Lift($L$) can be determined by Lift Coefficient ($C_L$) like the following equation.

#References

[1] J.Rodriguez. Whats New in Deep Learning Research: Understanding Federated Learning.